Composite structure having a variable gage and methods for forming a composite structure having a variable gage

ABSTRACT

In an example, a composite structure having a variable gage is described. The composite structure includes a first end having a first gage, a second end having a second gage, which is less than the first gage, a plurality of continuous plies, and a plurality of drop-off plies. Each continuous ply extends from the first end to the second end. Each drop-off ply includes a tip having a tapered shape. Each drop-off ply extends from the first end to a respective position of the tip of the drop-off ply between the first end and the second end. The tips of the plurality of drop-off plies are arranged in a monotonically-inward pattern.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 16/408,410, filed May 9, 2019, the contents of which is herebyincorporated by reference in its entirety.

FIELD

The present disclosure generally relates to composite structures and,more specifically, to composite structures and methods for formingcomposite structures having a variable gage.

BACKGROUND

Composite structures are used in a wide variety of applications,including in the manufacture of aircraft, spacecraft, rotorcraft,watercraft, automobiles, trucks, and other vehicles and structures, dueto their high strength-to-weight ratios, corrosion resistance, and otherfavorable properties. In general, a composite structure is a structurethat is formed from two or more constituent component materials withdifferent physical and/or chemical properties that, when combined,produce a composite material having characteristics that are differentthan the characteristics of the individual components materials.

As an example, one type of composite material is carbon fiber reinforcedplastic (“CFRP”). CFRP generally includes one or more composite layersor plies laminated together to form a sheet, laminate or layup. Each ofthe composite layers or plies can include a reinforcement material and amatrix material. The matrix material surrounds, binds and supports thereinforcement material. The reinforcement material provides structuralstrength to the matrix material and the CFRP. The matrix material isgenerally a non-conductive polymer such as an epoxy resin. Thereinforcement material generally consists of strands of carbon fiber,which are electrically conductive.

SUMMARY

In an example, a composite structure having a variable gage isdescribed. The composite structure includes a first end having a firstgage, a second end having a second gage, which is less than the firstgage, a first outer surface extending from the first end to the secondend, a second outer surface extending from the first end to the secondend, and a plurality of plies (i) extending between the first end andthe second end and (ii) arranged in a stack between the first outersurface and the second outer surface.

The plurality of plies include a plurality of continuous plies and aplurality of drop-off plies. Each continuous ply extends from the firstend to the second end. Each drop-off ply includes a tip having a taperedshape. Each drop-off ply extends from the first end to a respectiveposition of the tip of the drop-off ply between the first end and thesecond end. A first subset of the plurality of drop-off plies arebetween the first outer surface and a central portion of the stack and asecond subset of the plurality of drop-off plies are between the centralportion and the second outer surface. The tips of the plurality ofdrop-off plies are arranged in a monotonically-inward pattern including:(a) in a first order of the first subset of the plurality of drop-offplies from the first outer surface toward the central portion, with eachsuccessive drop-off ply in the first order, a relative distance betweenthe tip of the drop-off ply and the second end decreases, and (b) in asecond order of the second subset of the plurality of drop-off pliesfrom the second outer surface toward the central portion, with eachsuccessive drop-off ply in the second order, a relative distance betweenthe tip of the drop-off ply and the second end decreases.

In another example, a method of forming a composite structure having avariable gage is described. The method includes forming a plurality ofcontinuous plies and forming a plurality of drop-off plies. Forming theplurality of drop-off plies includes forming, for each drop-off ply, atip of the drop-off ply having a tapered shape. The method also includespositioning the plurality of continuous plies and the plurality ofdrop-off plies in a stack having (i) a first end, (ii) a second end,(iii) a first outer surface extending from the first end to the secondend, and (iv) a second outer surface extending from the first end to thesecond end. The first end has a first gage and the second end has asecond gage, which is less than the first gage.

Positioning the plurality of continuous plies and the plurality ofdrop-off plies includes positioning the plurality of continuous pliessuch that each continuous ply extends from the first end to the secondend, and positioning the plurality of drop-off plies such that eachdrop-off ply extends from the first end to a respective position of thetip of the drop-off ply between the first end and the second end. Afirst subset of the plurality of drop-off plies are between the firstouter surface and a central portion of the stack and a second subset ofthe plurality of drop-off plies are between the central portion and thesecond outer surface.

Positioning the plurality of continuous plies and the plurality ofdrop-off plies in the stack further comprises arranging the plurality ofdrop-off plies in a monotonically-inward pattern including: (a) in afirst order of the first subset of the plurality of drop-off plies fromthe first outer surface toward the central portion, with each successivedrop-off ply in the first order, a relative distance between the tip ofthe drop-off ply and the second end decreases, and (b) in a second orderof the second subset of the plurality of drop-off plies from the secondouter surface toward the central portion, with each successive drop-offply in the second order, a relative distance between the tip of thedrop-off ply and the second end decreases.

In another example, a composite structure having a variable gage isdescribed. The composite structure includes a first segment having afirst gage, a second segment having a second gage, which is less thanthe first gage, and a transition segment between the first segment andthe second segment. The transition segment includes a first end at thefirst segment and having the first gage, a second end at the secondsegment and having a second gage, a first outer surface extending fromthe first end to the second end, a second outer surface extending fromthe first end to the second end, and a plurality of plies (i) extendingbetween the first end and the second end and (ii) arranged in a stackbetween the first outer surface and the second outer surface.

The plurality of plies include a plurality of continuous plies and aplurality of drop-off plies. Each continuous ply extends from the firstend to the second end. Each drop-off ply includes a tip having a taperedshape. Each drop-off ply extends from the first end to a respectiveposition of the tip of the drop-off ply between the first end and thesecond end.

A first subset of the plurality of drop-off plies are between the firstouter surface and a central portion of the stack and a second subset ofthe plurality of drop-off plies are between the central portion and thesecond outer surface. The tips of the plurality of drop-off plies arearranged in a monotonically-inward pattern including: (a) in a firstorder of the first subset of the plurality of drop-off plies from thefirst outer surface toward the central portion, with each successivedrop-off ply in the first order, a relative distance between the tip ofthe drop-off ply and the second end decreases, and (b) in a second orderof the second subset of the plurality of drop-off plies from the secondouter surface toward the central portion, with each successive drop-offply in the second order, a relative distance between the tip of thedrop-off ply and the second end decreases.

The features, functions, and advantages that have been discussed can beachieved independently in various examples or may be combined in yetother examples further details of which can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE FIGURES

The novel features believed characteristic of the illustrative examplesare set forth in the appended claims. The illustrative examples,however, as well as a preferred mode of use, further objectives anddescriptions thereof, will best be understood by reference to thefollowing detailed description of an illustrative example of the presentdisclosure when read in conjunction with the accompanying drawings,wherein:

FIG. 1 depicts a composite structure, according to an example.

FIG. 2 depicts a composite structure, according to another example.

FIG. 3 depicts a composite structure, according to another example.

FIG. 4 depicts a simplified block diagram of a composite structure,according to another example.

FIG. 5A depicts a side view of a composite stringer including thecomposite structure of FIG. 1, according to another example.

FIG. 5B depicts a side view of a composite stringer including thecomposite structure of FIG. 3, according to another example.

FIG. 6 illustrates a flow chart of an example process for forming acomposite structure having a variable gage, according to an example.

FIG. 7 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 6.

FIG. 8 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 6.

FIG. 9 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 8.

FIG. 10 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 9.

FIG. 11 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 9.

FIG. 12 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 11.

FIG. 13 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 6.

FIG. 14 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 6.

FIG. 15 illustrates a flow chart of an example process for forming acomposite structure having a variable gage, according to an example.

FIG. 16 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 15.

FIG. 17 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 16.

FIG. 18 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 16.

FIG. 19 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 16.

FIG. 20 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 16.

FIG. 21 illustrates a flow chart of an example process for forming acomposite structure having a variable gage that can be used with theprocess shown in FIG. 16.

DETAILED DESCRIPTION

Disclosed examples will now be described more fully hereinafter withreference to the accompanying drawings, in which some, but not all ofthe disclosed examples are shown. Indeed, several different examples maybe described and should not be construed as limited to the examples setforth herein. Rather, these examples are described so that thisdisclosure will be thorough and complete and will fully convey the scopeof the disclosure to those skilled in the art.

By the term “approximately” or “substantially” with reference to amountsor measurement values described herein, it is meant that the recitedcharacteristic, parameter, or value need not be achieved exactly, butthat deviations or variations, including for example, tolerances,measurement error, measurement accuracy limitations and other factorsknown to those of skill in the art, may occur in amounts that do notpreclude the effect the characteristic was intended to provide.

As used herein, the terms “greater than” and “less than” are intended tohave their common meaning. Thus, a first value is greater than a secondvalue if the first value is greater than the second value by any amount.Similarly, a first value is less than a second value if the first valueis less than the second value by any amount.

As used herein, the term “composite structure” means a structure that ismanufactured, fabricated or assembled, in whole or in part, from one ormore composite materials.

As noted above, a composite structure can be used in a wide variety ofapplications, including in the manufacture of aircraft, spacecraft,rotorcraft, watercraft, flying taxis, trains, automobiles, trucks, andother vehicles (e.g., passenger capsules or cargo containers) due totheir high strength-to-weight ratios, corrosion resistance, and otherfavorable properties. Additionally or alternatively, a compositestructure can be used in buildings, bridges, swimming pools, storagetanks, robotic frame structures, energy structures (e.g., wind blades,turbine blades, propulsion blades, and/or solar panels), sporting goods(e.g., bicycle frames, skis, snow boards, surfing boards, paddies),residential houses, office buildings, and/or medical board frames.

In some implementations, different portions of a composite structure mayhave different gages. As used herein, the term “gage” means a thicknessbetween two opposing sides of the composite structure. It may bedesirable to vary the gage from one portion of the composite structurerelative to another portion of the composite structure for a variety ofreasons. For example, a stiffness and/or a strength of the compositestructure may be related to the gage of the composite structure. In someinstances, it may be desirable to vary the stiffness and/or the strengthof the composite structure from a first portion of the compositestructure to a second portion of the composite structure. For instance,the first portion of the composite structure may be expected toexperience a relatively greater amount of loading and/or applied forcethan the second portion of the composite structure. As such, it may bedesirable for the first portion of the composite structure to have agage that is greater than a gage of the second portion of the compositestructure.

In other examples, it may be desirable to vary the gage of the compositestructure additionally or alternatively based on other design criteriasuch as, for example, aesthetics, weight distribution, spaceconstraints, load variation, and/or damage protection.

One approach to transitioning from one gage to another gage involvesforming the composite structure from a plurality of plies of compositematerial, which include a plurality of continuous plies and one or moredrop-off plies. In general, each continuous ply extends from a first endto a second end of the composite structure. By contrast, each drop-offply extends from the first end to a respective position of a tip of thedrop-off ply between the first end and the second end. In thisarrangement, there are fewer plies at the second end relative to thefirst end. Thus, by positioning the tips of the drop-off plies betweenthe first end and the second end, the gage decreases from the first endto the second end so as to transition from one gage to another gage.

Existing approaches to transitioning from one gage to another gagesuffer from some drawbacks. For example, in existing compositestructuring having a variable gage, the tips of the drop-off plies havea blunt-end shape and are arranged immediately adjacent to each other ina cluster. This can result in a relatively large resin pocket in aregion at or near the tips of the drop-off plies. In some instances, therelatively large resin pocket may lead to delamination in the regionunder certain thermal and/or mechanical loads. Additionally, forexample, arranging the tips of the drop-off plies in a cluster mayincrease a risk of ply kinks and/or wrinkles, which may reduce laminatestrength.

As an example, FIG. 1 depicts an example composite structure 100 havinga variable gage, according to an example. As shown in FIG. 1, thecomposite structure 100 includes a first end 110A having a first gage112A and a second end 110B having a second gage 112B, which is less thanthe first gage 112A of the first end 110A. The composite structure 100also includes a first outer surface 114 extending from the first end110A to the second end 110B, and a second outer surface 116 extendingfrom the first end 110A to the second end 110B.

As also shown in FIG. 1, the composite structure 100 includes aplurality of plies 118 _(i=1) to 118 _(i=n) of composite material(hereinafter collectively referred to as “plies 118 _(i)”) arranged in astack between the second outer surface 116 and the first outer surface114, where n is an integer value that is greater than or equal to two.In FIG. 1, the composite structure 100 includes a total of 18 plies 118_(i) (i.e., n=18). However, in other examples, the composite structure100 can include a lesser quantity or a greater quantity of plies 118_(i).

In this arrangement, the first gage 112A of the first end 110A and thesecond gage 112B of the second end 110B are respective thicknessesbetween the first outer surface 114 and the second outer surface 116 atthe first end 110A and the second end 110B, respectively. Further, thefirst gage 112A is related to a quantity of the plies 118 _(i) at thefirst end 110A and the second gage 112B is related to a quantity of theplies 118 _(i) at the second end 110B. For instance, in FIG. 1, thequantity of the plies 118 _(i) at the first end 110A is greater than thequantity of the plies 118 _(i) at the second end 110B such that thefirst gage 112A is greater than the second gage 112B.

Specifically, to vary the quantity of the plies 118 _(i) between thefirst end 110A and the second end 110B, the plies 118 _(i) of compositematerial include a plurality of continuous plies 118A and a plurality ofdrop-off plies 118B. In FIG. 1, each continuous ply 118A extends fromthe first end 110A to the second end 110B. Whereas, each drop-off ply118B includes a tip 120, and each drop-off ply 118B extends from thefirst end 110A to a respective position of the tip 120 of the drop-offply 118B between the first end 110A and the second end 110B.

Accordingly, while the continuous plies 118A are present at the firstend 110A and the second end 110B, the drop-off plies 118B are present atthe first end 110A and absent at the second end 110B. In this way, thedrop-off plies 118B can contribute to the first gage 112A at the firstend 110A, whereas the drop-off plies 118B do not contribute to thesecond gage 112B at the second end 110B due to the drop-off plies 118Bterminating prior to the second end 110B (i.e., the tips 120 beinglocated at the respective positions between the first end 110A and thesecond end 110B).

For clarity of illustration, in FIG. 1, a representative subset of thecontinuous plies 118A are labeled with reference number 118A and arepresentative subset of the drop-off plies 118B are labeled withreference number 118B. However, each of the plies 118 _(i) that extendsentirely from the first end 110A to the second end 110B is one of thecontinuous plies 118A, and each of the plies 118 _(i) that terminatesbetween the first end 110A and the second end 110B is one of thedrop-off plies 118B. Specifically, in FIG. 1, the plies 118_(i=1-3, 9-18) are the continuous plies 118A, and the plies 118 _(i=4-8)are the drop-off plies 118B.

As shown in FIG. 1, the tip 120 of each drop-off ply 118B has ablunt-end shape, and the drop-off plies 118B are arranged immediatelynext to each other in the stack (e.g., in a cluster). In general, thisapproach to transitioning from one gage to another gage can beeffective. However, it has been found that the performance of thecomposite structure 100 can be improved using one or more of thetechniques described in detail below with respect to FIGS. 2-3.

For example, using drop-off plies 118B with blunt-end shaped tips 120and/or arranging the drop-off plies 118B in a cluster can result in arelatively large resin pocket in a region 122 at or near the tips 120 ofthe drop-off plies 118B. In some instances, the relatively large resinpocket in the region 122 may lead to delamination in the region 122under certain thermal and/or mechanical loads. Additionally, forexample, arranging the tips 120 of the drop-off plies 118B in a clustermay increase a risk of ply kinks and/or wrinkles, which may reducelaminate strength. Further, in some instances, arranging the tips 120 ofthe drop-off plies at an off-center location (e.g., closer to the firstouter surface 114 than the second outer surface 116) can also increase arisk of ply kinks and/or wrinkles, which can have a reduced staticstrength and/or a reduced fatigue strength due to potential distortionunder thermal and/or mechanical loads.

Within examples, composite structures having variable gages aredescribed, which can improve upon the composite structure 100 in one ormore respects. For instance, in some examples, the tips 120 of thedrop-off plies 118B can have a tapered shape and/or the plies 118 _(i)can be arranged according to one or more patterns that can, among otherthings, enhance the load bearing properties of a composite structure,reduce re-curing, simplify tooling requirements for forming thecomposite structure, reduce material handling costs, and/or reduce aweight of the composite structure.

Referring now to FIG. 2, a composite structure 200 having a variablegage is depicted according to an example. As shown in FIG. 2, thecomposite structure 200 includes a first end 210A having a first gage212A and a second end 210B having a second gage 212B, which is less thanthe first gage 212A of the first end 210A. Additionally, as shown inFIG. 2, the composite structure 200 includes a first outer surface 214extending from the first end 210A to the second end 210B, and a secondouter surface 216 extending from the first end 210A to the second end210B.

As also shown in FIG. 2, the composite structure 200 includes aplurality of plies 218 _(i=1) to 218 _(i=n) of composite material(hereinafter collectively referred to as “plies 218 _(i)”) arranged in astack between the second outer surface 216 and the first outer surface214, where n is an integer value that is greater than or equal to two.In FIG. 2, the composite structure 200 includes a total of 28 plies 218_(i) (i.e., n=28). However, in other examples, the composite structure200 can include a lesser quantity or a greater quantity of plies 218_(i).

In this arrangement, the first gage 212A of the first end 210A and thesecond gage 212B of the second end 210B are respective thicknessesbetween the first outer surface 214 and the second outer surface 216 atthe first end 210A and the second end 210B, respectively. Further, asdescribed above, the first gage 212A is related to a quantity of theplies 218 _(i) at the first end 210A and the second gage 212B is relatedto a quantity of the plies 218 _(i) at the second end 210B. Forinstance, in FIG. 2, the quantity of the plies 218 _(i) at the first end210A is greater than the quantity of the plies 218 _(i) at the secondend 210B such that the first gage 212A is greater than the second gage212B.

As described above, the variable gage of the composite structure 200results from the plies 218 _(i) of composite material including aplurality of continuous plies 218A and a plurality of drop-off plies218B arranged in the stack between the second outer surface 216 and thefirst outer surface 214. In FIG. 2, each continuous ply 218A extendsfrom the first end 210A to the second end 210B. Whereas, each drop-offply 218B extends from the first end 210A to a respective position of atip 220 of the drop-off ply 218B between the first end 210A and thesecond end 210B. Thus, the first gage 212A is based on a quantity of thecontinuous plies 218A and a quantity of the drop-off plies 218B, and thesecond gage 212B is based on the quantity of the continuous plies 218A(and not the quantity of the drop-off plies 218B).

For clarity of illustration, in FIG. 2, a representative subset of thecontinuous plies 218A are labeled with reference number 218A and arepresentative subset of the drop-off plies 218B are labeled withreference number 218B. However, each of the plies 218 _(i) that extendsentirely from the first end 210A to the second end 210B is one of thecontinuous plies 218A, and each of the plies 218 _(i) that terminatesbetween the first end 210A and the second end 210B is one of thedrop-off plies 218B. Specifically, in FIG. 2, the plies 218_(i=1-6, 8, 10, 12, 14, 15, 17, 19, 21, 23, 25-28) are the continuousplies 218A, and the plies 218 _(i=7, 9, 11, 13, 16, 18, 20, 22, 24) arethe drop-off plies 218B.

As shown in FIG. 2, the tip 220 of each drop-off ply 218B has a taperedshape. More particularly, for example, the tip 220 of each drop-off ply218B can gradually reduce in thickness in a direction along the tip 220from the first end 210A toward the second end 210B. Because the tip 220has the tapered shape, the tip 220 can more closely abut againstadjacent ones of the plies 218 _(i) (e.g., as compared to the blunt-endshaped tips 120 in FIG. 1, which terminate relatively abruptly). Assuch, the tips 220 having the tapered shape can reduce (or may minimize)resin pockets at the tips 220 of the drop-off plies 218B, which can helpto improve (or may maximize) interlaminar strength of the compositestructure 200. Accordingly, the tapered shape of the tips 220 of thedrop-off plies 218B can help to improve a load bearing performance ofthe composite structure 200 having the variable gage for transitioningfrom a section having the first gage 212A to a section having the secondgage 212B.

Within examples, the tapered shape of the tips 220 of the drop-off plies218B can be formed by cutting each drop-off ply 218B at an angle lessthan approximately 85 degrees relative to a longitudinal axis of thedrop-off ply 218B. By contrast, the blunt-end shape of the tips 120 ofthe drop-off plies 118B shown in FIG. 1 can be formed, for example, bycutting each drop-off ply 118B at an angle of approximately 90 degreesrelative to a longitudinal axis of the drop-off ply 118B.

As noted above, the load bearing performance of the composite structure200 can be enhanced, additionally or alternatively, based on a patternin which the plies 218 _(i) are arranged in the composite structure 200.For example, in FIG. 2, the drop-off plies 218B are separated from eachother by at least one of the continuous plies 218A. More particularly,in FIG. 2, each drop-off ply 218B is sandwiched between and abutsagainst a respective two continuous plies 218A of the plurality ofcontinuous plies 218A. By separating the drop-off plies 218B from eachother and/or sandwiching the drop-off plies 218B between the continuousplies 218A, the drop-off plies 218B can be more uniformly distributedbetween the second outer surface 216 and the first outer surface 214 (ascompared to the clustered arrangement of the drop-off plies 118B shownin FIG. 1). This can help to reduce (or may prevent) ply kinks and/orwrinkles, reduce (or may prevent) resin pockets, and/or increase (or maymaximize) interlaminar strength of the composite structure 200.

As noted above, in FIG. 2, the plies 218_(i=1-6, 8, 10, 12, 14, 15, 17, 19, 21, 23, 25-28) are the continuousplies 218A, and the plies 218 _(i=7, 9, 11, 13, 16, 18, 20, 22, 24) arethe drop-off plies 218B. Accordingly, in FIG. 2, each of the plies 218_(i=7, 9, 11, 13, 16, 18, 20, 22, 24) is separated from each other by atleast one of the plies 218_(i=1-6, 8, 10, 12, 14, 15, 17, 19, 21, 23, 25-28), and each of theplies 218 _(i=7, 9, 11, 13, 16, 18, 20, 22, 24) is sandwiched betweenand abuts against a respective two of the plies 218_(i=1-6, 8, 10, 12, 14, 15, 17, 19, 21, 23, 25-28). For instance, inFIG. 2, the ply 218 _(i=7) is separated from the ply 218 _(i=9) by theply 218 _(i=8), and the ply 218 _(i=7) is sandwiched between the ply 218_(i=6) and the ply 218 _(i=8). Additionally, for instance, the ply 218_(i=9) is separated from the ply 218 _(i=11) by the ply 218 _(i=10),separated from the ply 218 _(i=9) by the ply 218 _(i=8), and sandwichedbetween the ply 218 _(i=8) and the ply 218 _(i=10). Further, forinstance, the ply 218 _(i=16) is separated from the ply 218 _(i=13) bythe plies 218 _(i=14, 15), separated from the ply 218 _(i=18) by the ply218 _(i=17), and sandwiched between the ply 218 _(i=15) and the ply 218_(i=17). Similar relationships exist for a remainder of the drop-offplies 218B in FIG. 2 (i.e., the plies 218 _(i=11, 13, 18, 20, 22, 24)).As noted above, arranging the plies 218 _(i) in a pattern having acharacteristic of the drop-off plies 218B interleaved with thecontinuous plies 218A (e.g., as shown in FIG. 2) can help to reduce (ormay prevent) ply kinks and/or wrinkles, reduce (or may prevent) resinpockets, and/or increase (or may maximize) interlaminar strength of thecomposite structure 200.

Within examples, the pattern of the tips 220 of the drop-off plies 218Bcan additionally or alternatively include one or more of the followingcharacteristics: (i) an arrangement of the tips 220 in a first half ofthe composite structure 200 in a pattern that substantially mirrors ormirrors a pattern of the tips 220 in a second half of the compositestructure 200, (ii) a staggered arrangement of the tips 220 relative toeach other, and/or (iii) spacing the tips 220 relative to each other byat least one threshold distance (e.g., at least one distance related torespective positions and/or respective thicknesses of one or more of theplies 218). Each of these characteristics alone or in combination cancontribute to arranging the drop-off plies 218B in a pattern that canreduce (or may prevent) ply kinks and/or wrinkles, reduce (or mayprevent) resin pockets, and/or increase (or may maximize) interlaminarstrength.

FIG. 2 shows the tips 220 arranged in substantially mirror or mirrorpatterns relative to a central portion 224 of the composite structure200 according to one example. The central portion 224 can include one ormore of the plies 218 _(i) that provide a frame of reference forcharacterizing patterns of the tips 220 of the drop-off plies 218B onopposing sides of the central portion 224. In general, the centralportion 224 (i) is between the second outer surface 216 and the firstouter surface 214 and (ii) extends from the first end 210A to the secondend 210B.

In FIG. 2, the central portion 224 can include the plies 218_(i=15, 16). Thus, in FIG. 2, the central portion 224 can include asingle drop-off ply 218B (i.e., the ply 218 _(i=16)) and a singlecontinuous ply 218A (i.e., the ply 218 _(i=15)). However, in anotherexample, the central portion 224 can include two drop-off plies 218B andat least one continuous ply 218A. In yet another example, the centralportion 224 can consist of only a single drop-off ply 218B. In anotherexample, the central portion 224 can consist of one or more continuousplies 218A and omit the drop-off plies 218B. More generally, the centralportion 224 can include one or more of the continuous plies 218A and/orone or more of the drop-off plies 218B.

As noted above, the tips 220 of the drop-off plies 218B can be arrangedin substantially mirror or mirror patterns relative to the centralportion 224. For instance, a first subset of the drop-off plies 218B canbe between the first outer surface 214 and the central portion 224, anda second subset of the drop-off plies 218B can be between the centralportion 224 and the second outer surface 216. In this arrangement, thetips 220 of the first subset of the drop-off plies 218B are arranged ina pattern that substantially mirrors a pattern of the tips 220 of thesecond subset of the drop-off plies 218B. In other words, with referenceto the central portion 224, the respective positions of the tips 220 ofthe first subset of the drop-off plies 218B are (i) reversely and (ii)similarly (or identically) arranged in comparison to the respectivepositions of the tips 220 of the second subset of the drop-off plies218B.

For example, in FIG. 2, the central portion 224 can include the plies218 _(i=15, 16), the first subset of the drop-off plies 218B can includethe plies 218 _(i=7, 9, 11, 13), and the second subset of the drop-offplies 218B can include the plies 218 _(i=18, 20, 22, 24). As shown inFIG. 2, the pattern of the tips 220 of the first subset of the drop-offplies 218B substantially mirrors the pattern of the tips 220 of thesecond subset of the drop-off plies 218B. For instance, with referenceto the central portion 224, the respective positions of the tips 220 ofthe first subset are reversely and similarly arranged in comparison tothe respective positions of the tips 220 of the second subset.

Additionally, as shown in FIG. 2, the pattern of the tips 220 of thedrop-off plies 218B can be a monotonically-outward pattern. Forinstance, in FIG. 2, the first subset of the drop-off plies 218B can bein an order from a drop-off ply 218B closest to the central portion 224(e.g., the ply 218 _(i=13)) to a drop-off ply 218B closest to the firstouter surface 214 (i.e., the ply 218 _(i=7)). The pattern of the tips220 of the first subset of the drop-off plies 218B can include, witheach successive drop-off ply 218B in the order, a relative distancebetween the tip 220 of the drop-off ply 218B and the second end 210Bdecreases. As such, in FIG. 2, (i) the tip 220 of the ply 218 _(i=13) isat a first distance from the second end 210B, (ii) the tip 220 of theply 218 _(i=11) is at a second distance from the second end 210B, whichis less than the first distance, (iii) the tip 220 of the ply 218 _(i=9)is at a third distance from the second end 210B, which is less than thesecond distance, and (iv) the tip 220 of the ply 218 _(i=7) is at afourth distance from the second end 210B, which is less than the thirddistance.

Similarly, the second subset of the drop-off plies 218B can be in anorder from a drop-off ply 218B closest to the central portion 224 (e.g.,the ply 218 _(i=18)) to a drop-off ply 218B closest to the second outersurface 216 (e.g., the ply 218 _(i=24)). The pattern of the tips 220 ofthe second subset of the drop-off plies 218B includes, with eachsuccessive drop-off ply 218B in the order, a relative distance betweenthe tip 220 of the drop-off ply 218B and the second end 210B decreases.As such, in FIG. 2, (v) the tip 220 of the ply 218 _(i=18) is at a fifthdistance from the second end 210B, (vi) the tip 220 of the ply 218_(i=20) is at a sixth distance from the second end 210B, which is lessthan the fifth distance, (vii) the tip 220 of the ply 218 _(i=22) is ata seventh distance from the second end 210B, which is less than thesixth distance, and (viii) the tip 220 of the ply 218 _(i=24) is at aneighth distance from the second end 210B, which is less than the seventhdistance.

Accordingly, in the monotonically-outward pattern of the tips 220 shownin FIG. 2, the tips 220 of the drop-off plies 218B generally appear tobe spread outward from the central portion 224 in a direction from thefirst end 210A to the second end 210B. The monotonically-outward patternof the tips 220 can help to more gradually and/or smoothly transitionfrom the first gage 212A at the first end 210A to the second gage 212Bat the second end 210B. Additionally, for example, themonotonically-outward pattern of the tips 220 can help to achieve arelatively greater degree of symmetry relative to, for instance, thearrangement of the tips 120 in FIG. 1 (which are clustered near thefirst outer surface 114).

According to an additional or alternative aspect of themonotonically-outward pattern shown in FIG. 2, the drop-off plies 218Bcan be arranged in a plurality of pairs of drop-off plies 218B thatdefine an order in which the drop-off plies 218B drop off in a directionfrom the first end 210A toward the second end 210B (i.e., an order ofthe respective positions of the tips 220 in the direction from the firstend 210A toward the second end 210B). In particular, each pair ofdrop-off plies 218B can include a respective one drop-off ply 218B ofthe first subset and a respective one drop-off ply 218B of the secondsubset.

For example, in FIG. 2, a first pair includes the plies 218 _(i=13, 18),a second pair includes the plies 218 _(i=11, 20), a third pair includesthe plies 218 _(i=9, 22), and a fourth pair includes the plies 218_(i=7, 24). As shown in FIG. 2, in the direction from the first end 210Ato the second end 210B, the drop-off plies 218B drop off in an orderfrom the first pair to the fourth pair. In other words, the tips 220 ofthe first pair of the drop-off plies 218B are closest to the first end210A, the tips 220 of the second pair of the drop-off plies 218B aresecond closest to the first end 210A, the tips 220 of the third pair ofthe drop-off plies 218B are third closest to the first end 210A, and thetips 220 of the fourth pair of the drop-off plies 218B are farthest fromthe first end 210A.

Additionally, for example, for each pair of drop-off plies 218B, therespective one drop-off ply 218B of the first subset and the respectiveone drop-off ply 218B of the second subset can be substantiallyequidistant from the central portion 224 in a dimension between thefirst outer surface 214 and the second outer surface 216. For instance,as shown in FIG. 2, the first pair of the drop-off plies 218B are eachspaced from the central portion 224 by a distance equal to a plythickness 226 of a single ply 218 _(i), the second pair of the drop-offplies 218B are each spaced from the central portion 224 by a distanceequal to three times the ply thickness 226, the third pair of thedrop-off plies 218B are each spaced from the central portion 224 by adistance equal to five times the ply thickness 226, and the fourth pairof the drop-off plies 218B are each spaced from the central portion 224by a distance equal to seven times the ply thickness 226. Arranging thedrop-off plies 218B in pairs that (i) drop off, pair-by-pair, in anorder from the first end 210A to the second end 210B, and/or (ii) areequidistant relative to the central portion 224 can additionally help tomore gradually and/or smoothly transition from the first gage 212A atthe first end 210A to the second gage 212B at the second end 210B,and/or achieve a relatively greater degree of symmetry relative to, forinstance, the arrangement of the tips 120 in FIG. 1 (which are clusterednear the first outer surface 114).

Within examples, each drop-off ply 218B can have a ply angle, relativeto a longitudinal axis of the composite structure 200 (e.g., thelongitudinal axis 348), which is between approximately −30 degrees and+30 degrees. This can help to achieve a desired stiffness with arelatively few (or minimal) quantity of plies 218 _(i) and, thus, reduce(or may minimize) a weight and/or cost of fabricating the compositestructure 200. In an example, for each pair, the ply angle isapproximately the same for the drop-off plies 218B of the pair. This canhelp to improve (or may maximize) a symmetry of the composite structure200.

According to an additional or alternative aspect of themonotonically-outward pattern shown in FIG. 2, the monotonically-outwardpattern can include, along a direction from the first end 210A to thesecond end 210B, the tips 220 of the first subset of the drop-off plies218B alternating with the tips 220 of the second subset of the drop-offplies 218B. For example, in FIG. 2, the tips 220 of the drop-off plies218B are in the following order from the first end 210A to the secondend 210B: (i) the tip 220 of the ply 218 _(i=18) from the second subset,(ii) the tip 220 of the ply 218 _(i=13) from the first subset, (iii) thetip 220 of the ply 218 _(i=20) from the second subset, (iv) the tip 220of the ply 218 _(i=11) from the first subset, (v) the tip 220 of the ply218 _(i=22) from the second subset, (vi) the tip 220 of the ply 218_(i=9) from the first subset, (vii) the tip 220 of the ply 218 _(i=24)from the second subset, and (viii) the tip 220 of the ply 218 _(i=7)from the first subset. Alternating the respective positions of the tips220 of the drop-off plies 218B can additionally or alternatively help tohelp to more gradually and/or smoothly transition from the first gage212A at the first end 210A to the second gage 212B at the second end210B.

As noted above, arranging the drop-off plies 218B such that the tips 220of the drop-off plies 218B are staggered relative to each other canadditionally or alternatively help to reduce (or may prevent) ply kinksand/or wrinkles, reduce (or may prevent) resin pockets, and/or increase(or may maximize) interlaminar strength. As an example, in FIG. 2, therespective positions of the tips 220 of the drop-off plies 218B can bestaggered from the first end 210A to the second end 210B. By“staggered”, it is meant that the tips 220 of the drop-off plies 218Bare each at a respective distance from the second end 210B, and therespective distances between the tips 220 and the second end 210B areall different from each other (i.e., the tips of no two drop-off pliesare equidistant from the second end 210B). Staggering the tips 220 ofthe drop-off plies 218B can help to mitigate some or all of thechallenges associated with a clustered arrangement of drop-off pliesdescribed above.

Also, as noted above, spacing the tips 220 relative to each other by atleast one threshold distance can additionally or alternatively help toreduce (or may prevent) ply kinks and/or wrinkles, reduce (or mayprevent) resin pockets, and/or increase (or may maximize) interlaminarstrength. In an example, for each drop-off ply 218B, a distance 228between the tip 220 of the drop-off ply 218B and the tip 220 of anadjacent one of the drop-off plies 218B can be at least ten timesgreater than the ply thickness 226 of the drop-off ply 218B. In thisexample, for each drop-off ply 218B, the adjacent one of the drop-offplies 218B is adjacent to the drop-off ply 218B in a dimension extendingbetween the first outer surface 214 and the second outer surface 216.That is, two of the drop-off plies 218B are adjacent to each other onlyif there is not another one of the drop-off plies 218B between the twoof the drop-off plies 218B in the dimension extending between the firstouter surface 214 and the second outer surface 216. Thus, for example,the ply 218 _(i=18) is adjacent to the ply 218 _(i=16) and the ply 218_(i=20), and non-adjacent to the other drop-off plies 218B (i.e., plies218 _(i=7, 9, 11, 13, 22, 24)).

A representative one of the distances 228 is depicted in FIG. 2 betweenthe tips 220 of the ply 218 _(i=18) and the ply 218 _(i=16), which areadjacent to each other. As shown in FIG. 2, the distance 228 between thetip 220 of the ply 218 _(i=18) and the tip of the ply 218 _(i=16) is atleast ten times greater than the ply thickness 226 of the ply 218_(i=18). Similarly, in FIG. 2, the tips 220 of the other adjacent onesof the drop-off plies 218B are separated by respective distances 228that are at least ten times greater than the ply thickness 226. Asdescribed above, arranging the drop-off plies 218B such that the tips220 of adjacent ones of the drop-off plies 218B are separated by thedistance 228 of at least ten times the ply thickness 226 can help toreduce (or may prevent) ply kinks and/or wrinkles, reduce (or mayprevent) resin pockets, and/or increase (or may maximize) interlaminarstrength.

Additionally or alternatively, for example, a distance 230 betweennon-adjacent ones of the drop-off plies 218B can be at least three timesgreater than the ply thickness 226 of each drop-off ply 218B. Arepresentative one of the distances 230 is depicted in FIG. 2 betweenthe tips 220 of the ply 218 _(i=18) and the ply 218 _(i=13), which arenon-adjacent to each other (e.g., because the ply 218 _(i=16) is betweenthe ply 218 _(i=18) and the ply 218 _(i=13)). As shown in FIG. 2, thedistance 230 between the tip 220 of the ply 218 _(i=18) and the tip ofthe ply 218 _(i=13) is at least three times greater than the plythickness 226 of the ply 218 _(i=18). Similarly, the tips 220 of theother non-adjacent ones of the drop-off plies 218B are separated byrespective distances 230 that are at least three times greater than theply thickness 226. As described above, arranging the drop-off plies 218Bsuch that the tips 220 of non-adjacent ones of the drop-off plies 218Bare separated by the distance 228 of at least three times the plythickness 226 can help to reduce (or may prevent) ply kinks and/orwrinkles, reduce (or may prevent) resin pockets, and/or increase (or maymaximize) interlaminar strength.

In FIG. 2, the ply thickness 226 is the same for all of the plies 218_(i). However, in another example, one or more of the plies 218 _(i) canhave a different ply thickness than another one of the plies 218 _(i).In some implementations, providing the plies 218 _(i) with different plythicknesses can help to provide relatively greater flexibility forachieving fabrication quality objectives.

Additionally, in FIG. 2, the tips 220 of the drop-off plies 218B allhave the tapered shape. However, in another example, one or more of thetips 220 of the drop-off plies 218B can have the blunt-end shape shownin FIG. 1. Although the tapered shape can be beneficial for at least thereasons described above, a composite structure including the drop-offplies 218B having the tips 120 with the blunt-end shape in a patternhaving one or more of the characteristics described above with respectto FIG. 2 can provide improvements over the composite structure 100shown in FIG. 1. Similarly, a composite structure including the drop-offplies 118B arranged in the pattern shown in FIG. 1, but with the tips220 having the tapered shape can provide improvements over the compositestructure 100 shown in FIG. 1. Accordingly, within examples, thedrop-off plies 118B, 218B can the tips 220 with the tapered shape and/orthe tips 120 with the blunt-end shape, and the drop-off plies 118B, 218Bcan be arranged in a clustered pattern (as shown in FIG. 1) and/or apattern having one or more of the characteristics described above withrespect to FIG. 2.

As described, arranging the tips 220 of the drop-off plies 218B in apattern having one or more of the characteristics described above canhelp to achieve a relatively greater degree of symmetry for thecomposite structure 200 (e.g., about the central portion 224) relativeto, for instance, the arrangement of the tips 120 in FIG. 1. As usedherein, the term “symmetry” is intended to be a relative term and doesnot mean exactly symmetric. For example, as shown in FIG. 2, thecomposite structure 200 includes 14 plies 218 _(i) between the centralportion 224 and the first outer surface 214, and 12 plies 218 _(i)between the central portion 224 and the second outer surface 216.However, in the context of this disclosure, the composite structure 200shown in FIG. 2 has a greater degree of symmetry relative to thecomposite structure 100 shown in FIG. 1.

Within examples, providing the composite structure 200 with a relativelygreater degree of symmetry about the central portion 224 can help toincrease (or may maximize) interlaminar strength. Additionally oralternatively, providing the composite structure 200 with a relativelygreater degree of symmetry about the central portion 224 can help toreduce (or may minimize) re-curing, tooling, material handling costs,and/or weight.

As described above, FIG. 2 shows the composite structure 200 with thedrop-off plies 218B arranged in an example pattern having one or morecharacteristics that can help to improve performance, reduce re-curing,reduce tooling, reduce material handling costs, and/or reduce a weightof the composite structure 200. Other example patterns having the one ormore characteristics are also possible.

For instance, FIG. 3 shows a composite structure 300 having a variablegage according to another example. As shown in FIG. 3, the compositestructure 300 includes a first end 310A having a first gage 312A and asecond end 310B having a second gage 312B, which is less than the firstgage 312A of the first end 310A. Additionally, as shown in FIG. 3, thecomposite structure 300 includes a first outer surface 314 extendingfrom the first end 310A to the second end 310B, and a second outersurface 316 extending from the first end 310A to the second end 310B.

As also shown in FIG. 3, the composite structure 300 includes aplurality of plies 318 _(i=1) to 318 _(i=n) of composite material(hereinafter collectively referred to as “plies 318 _(i)”) arranged in astack between the second outer surface 316 and the first outer surface314, where n is an integer value that is greater than or equal to two.In FIG. 3, the composite structure 300 includes a total of 28 plies 318_(i) (i.e., n=28). However, in other examples, the composite structure300 can include a lesser quantity or a greater quantity of plies 318_(i).

In this arrangement, the first gage 312A of the first end 310A and thesecond gage 312B of the second end 310B are respective thicknessesbetween the second outer surface 316 and the first outer surface 314 atthe first end 310A and the second end 310B, respectively. Further, thefirst gage 312A is related to a quantity of the plies 318 _(i) at thefirst end 310A and the second gage 312B is related to a quantity of theplies 318 _(i) at the second end 310B. For instance, in FIG. 3, thequantity of the plies 318 _(i) at the first end 310A is greater than thequantity of the plies 318 _(i) at the second end 310B such that thefirst gage 312A is greater than the second gage 312B.

As described above, the variable gage of the composite structure 300results from the plies 318 _(i) of composite material including aplurality of continuous plies 318A and a plurality of drop-off plies318B arranged in the stack between the second outer surface 316 and thefirst outer surface 314. In FIG. 3, each continuous ply 318A extendsfrom the first end 310A to the second end 310B. Whereas, each drop-offply 318B includes a tip 320, and each drop-off ply 318B extends from thefirst end 310A to a respective position of the tip 320 of the drop-offply 318B between the first end 310A and the second end 310B.

For clarity of illustration, in FIG. 3, a representative subset of thecontinuous plies 318A are labeled with reference number 318A and arepresentative subset of the drop-off plies 318B are labeled withreference number 318B. However, each of the plies 318 _(i) that extendsentirely from the first end 310A to the second end 310B is one of thecontinuous plies 318A, and each of the plies 318 _(i) that terminatesbetween the first end 310A and the second end 310B is one of thedrop-off plies 318B. Specifically, in FIG. 3, the plies 318_(i=1-4,6,8,10,12,14,15,17,19,21,23,25-28) are the continuous plies318A, and the plies 318 _(i=5,7,9,11,13,16,18,20,22,24) are the drop-offplies 318B.

As shown in FIG. 3, the tip 320 of each drop-off ply 318B has thetapered shape described above with respect to the tips 220 shown in FIG.2. As such, the tips 320 having the tapered shape can reduce (or mayminimize) resin pockets at the tips 320 of the drop-off plies 318B,which can help to improve (or may maximize) interlaminar strength of thecomposite structure 300. However, in other examples, one or more of thedrop-off plies 318B can have the blunt-end shape shown in FIG. 1.

As noted above, the load bearing performance of the composite structure300 can be enhanced, additionally or alternatively, based on the patternin which the plies 318 _(i) are arranged in the composite structure 300.For example, in FIG. 3, the drop-off plies 218B can be separated fromeach other by at least one of the continuous plies 318A. For instance,each drop-off ply 318B can be sandwiched between and abut against arespective two continuous plies 318A of the plurality of continuousplies 318A. By separating the drop-off plies 318B from each other and/orsandwiching the drop-off plies 318B between the continuous plies 318A,the drop-off plies 318B can be more uniformly distributed between thesecond outer surface 316 and the first outer surface 314 (as compared tothe clustered arrangement of the drop-off plies 118B shown in FIG. 1).This can help to reduce (or may prevent) ply kinks and/or wrinkles,reduce (or may prevent) resin pockets, and/or increase (or may maximize)interlaminar strength of the composite structure 300.

Within examples, the pattern of the tips 320 of the drop-off plies 218Bcan additionally or alternatively include one or more of the followingcharacteristics: (i) an arrangement of the tips 320 in a first half ofthe composite structure 300 in a pattern that mirrors a pattern of thetips 320 in a second half of the composite structure 300, (ii) astaggered arrangement of the tips 320 relative to each other, and/or(iii) spacing the tips 320 relative to each other by at least onethreshold distance. As described above, each of these characteristicsalone or in combination can contribute to arranging the drop-off plies318B in a pattern that can reduce (or may prevent) ply kinks and/orwrinkles, may reduce (or may prevent) resin pockets, and/or increase (ormay maximize) interlaminar strength.

FIG. 3 shows the tips 320 arranged in mirror patterns relative to acentral portion 324 of the composite structure 300 according to anotherexample. The central portion 324 can include one or more of the plies318 _(i) that provide a frame of reference for characterizing patternsof the tips 320 of the drop-off plies 318B on opposing sides of thecentral portion 324. As noted above, in general, the central portion 324(i) is between the second outer surface 316 and the first outer surface314 and (ii) extends from the first end 310A to the second end 310B.

In FIG. 3, the central portion 324 can include the plies 318_(i=14, 15). Thus, in FIG. 3, the central portion 324 can include twocontinuous plies 318A. However, in another example, the central portion324 can include two drop-off plies 318B and at least one continuous ply318A. In yet another example, the central portion 324 can consist ofonly a single drop-off ply 318B. In another example, the central portion324 can consist of at least one continuous ply 318A and omit thedrop-off plies 318B. More generally, the central portion 324 can includeone or more of the continuous plies 318A and/or one or more of thedrop-off plies 318B.

Also, as shown in FIG. 3, the tips 320 of the drop-off plies 318B can bearranged in substantially mirror or mirror patterns relative to thecentral portion 324. For instance, a first subset of the drop-off plies318B can be between the first outer surface 314 and the central portion324, and a second subset of the drop-off plies 318B can be between thecentral portion 324 and the second outer surface 316. In thisarrangement, the tips 320 of the first subset of the drop-off plies 318Bare arranged in a pattern that substantially mirrors a pattern of thetips 320 of the second subset of the drop-off plies 318B. In otherwords, with reference to the central portion 324, the respectivepositions of the tips 320 of the first subset of the drop-off plies 318Bare (i) reversely and (ii) similarly (or identically) arranged incomparison to the respective positions of the tips 320 of the secondsubset of the drop-off plies 318B.

For example, in FIG. 3, the central portion 324 can include the plies318 _(i=14, 15), the first subset of the drop-off plies 318B can includethe plies 318 _(i=5, 7, 9, 11, 13), and the second subset of thedrop-off plies 318B can include the plies 318 _(i=16, 18, 20, 22, 24).As shown in FIG. 3, the pattern of the tips 320 of the first subset ofthe drop-off plies 318B substantially mirrors the pattern of the tips320 of the second subset of the drop-off plies 318B. For instance, withreference to the central portion 324, the respective positions of thetips 320 of the first subset are reversely and similarly arranged incomparison to the respective positions of the tips 320 of the secondsubset.

As described above, FIG. 2 shows the pattern of the tips 220 of thedrop-off plies 218B as a monotonically-outward pattern. FIG. 3 shows thetips 320 of the drop-off plies 318B arranged in a monotonically-inwardpattern, according to an example. In a first order of the first subsetof the drop-off plies 318B from the first outer surface 314 toward thecentral portion 324, with each successive drop-off ply 318B in the firstorder, a relative distance between the tip 320 of the drop-off ply 318Band the second end 310B decreases. Also, in a second order of the secondsubset of the drop-off plies 318B from the second outer surface 316toward the central portion 324, with each successive drop-off ply 318Bin the second order, a relative distance between the tip 320 of thedrop-off ply 318B and the second end 310B decreases.

As such, in FIG. 3, (i) the tip 320 of the ply 218 _(i=5) is at a firstdistance from the second end 310B, (ii) the tip 320 of the ply 318_(i=7) is at a second distance from the second end 310B, which is lessthan the first distance, (iii) the tip 320 of the ply 318 _(i=9) is at athird distance from the second end 310B, which is less than the seconddistance, (iv) the tip 320 of the ply 318 _(i=11) is at a fourthdistance from the second end 310B, which is less than the thirddistance, and (v) the tip 320 of the ply 318 _(i=13) is at a fifthdistance from the second end 310B, which is less than the fourthdistance. Also, in FIG. 3, (vi) the tip 320 of the ply 318 _(i=24) is ata sixth distance from the second end 310B, (vii) the tip 320 of the ply318 _(i=22) is at a seventh distance from the second end 310B, which isless than the sixth distance, (viii) the tip 320 of the ply 318 _(i=20)is at an eighth distance from the second end 310B, which is less thanthe seventh distance, (ix) the tip 320 of the ply 318 _(i=18) is at aninth distance from the second end 310B, which is less than the eighthdistance, and (x) the tip 320 of the ply 318 _(i=16) is at a tenthdistance from the second end 310B, which is less than the ninthdistance.

Accordingly, in the monotonically-inward pattern of the tips 320 shownin FIG. 3, the tips 320 of the drop-off plies 318B generally appear tobe converge inward from the first outer surface 314 and the second outersurface 316 toward the central portion 324 in a direction from the firstend 310A to the second end 310B. The monotonically-inward pattern of thetips 320 can help to more gradually and/or smoothly transition from thefirst gage 312A at the first end 310A to the second gage 312B at thesecond end 310B. Additionally, for example, the monotonically-inwardpattern of the tips 320 can help to achieve a relatively greater degreeof symmetry relative to, for instance, the arrangement of the tips 120in FIG. 1 (which are clustered near the first outer surface 114).

According to an additional or alternative aspect of themonotonically-inward pattern shown in FIG. 3, the drop-off plies 318Bcan be arranged in a plurality of pairs of drop-off plies 318B thatdefine an order in which the drop-off plies 318B drop off in a directionfrom the first end 310A toward the second end 310B (i.e., an order ofthe respective positions of the tips 320 in the direction from the firstend 310A toward the second end 310B). In particular, each pair ofdrop-off plies 318B can include a respective one drop-off ply 318B ofthe first subset and a respective one drop-off ply 318B of the secondsubset.

For example, in FIG. 3, a first pair includes the plies 318 _(i=5, 24),a second pair includes the plies 318 _(i=7, 22), a third pair includesthe plies 318 _(i=9, 20), a fourth pair includes the plies 318_(i=11, 18), and a fifth pair includes the plies 318 _(i=13, 16). Asshown in FIG. 3, in the direction from the first end 310A to the secondend 310B, the drop-off plies 318B drop off in an order from the firstpair to the fifth pair. In other words, the tips 320 of the first pairof the drop-off plies 318B are closest to the first end 310A, the tips320 of the second pair of the drop-off plies 318B are second closest tothe first end 310A, the tips 320 of the third pair of the drop-off plies318B are third closest to the first end 310A, the tips 320 of the fourthpair of the drop-off plies 318B are second farthest from the first end310A, and the tips 320 of the fifth pair of the drop-off plies 318B arefarthest from the first end 310A.

Additionally, for example, for each pair of drop-off plies 318B, therespective one drop-off ply 318B of the first subset and the respectiveone drop-off ply 318B of the second subset can be equidistant from thecentral portion 324 in a dimension between the first outer surface 314and the second outer surface 316. For instance, as shown in FIG. 3, thefirst pair of the drop-off plies 318B are each spaced from the centralportion 324 by a distance equal to eight times a ply thickness 326 of asingle ply 318 _(i), the second pair of the drop-off plies 318B are eachspaced from the central portion 324 by a distance equal to six times theply thickness 326, the third pair of the drop-off plies 318B are eachspaced from the central portion 324 by a distance equal to four timesthe ply thickness 326, the fourth pair of the drop-off plies 318B areeach spaced from the central portion 324 by a distance equal to twotimes the ply thickness 326, and the fifth pair of the drop-off plies318B are each immediately adjacent to and abut against the centralportion 324. Arranging the drop-off plies 318B in pairs that (i) dropoff, pair-by-pair, in an order from the first end 310A to the second end310B, and/or (ii) are equidistant relative to the central portion 324can additionally help to more gradually and/or smoothly transition fromthe first gage 312A at the first end 310A to the second gage 312B at thesecond end 310B, and/or achieve a relatively greater degree of symmetryrelative to, for instance, the arrangement of the tips 120 in FIG. 1(which are clustered near the first outer surface 114).

According to an additional or alternative aspect of themonotonically-inward pattern shown in FIG. 3, the monotonically-inwardpattern can include, along a direction from the first end 310A to thesecond end 310B, the tips 320 of the first subset of the drop-off plies318B alternating with the tips 320 of the second subset of the drop-offplies 318B. For example, in FIG. 3, the tips 320 of the drop-off plies318B are in the following order from the first end 310A to the secondend 310B: (i) the tip 320 of the ply 318 _(i=5) from the first subset,(ii) the tip 320 of the ply 318 _(i=24) from the second subset, (iii)the tip 320 of the ply 318 _(i=7) from the first subset, (iv) the tip320 of the ply 318 _(i=22) from the second subset, (v) the tip 320 ofthe ply 318 _(i=9) from the first subset, (vi) the tip 320 of the ply318 _(i=20) from the second subset, (vii) the tip 320 of the ply 318_(i=11) from the first subset, (viii) the tip 320 of the ply 318 _(i=18)from the second subset, (ix) the tip 320 of the ply 318 _(i=13) from thefirst subset, and (x) the tip 320 of the ply 318 _(i=16) from the secondsubset. Alternating the respective positions of the tips 320 of thedrop-off plies 318B can additionally or alternatively help to help tomore gradually and/or smoothly transition from the first gage 312A atthe first end 310A to the second gage 312B at the second end 310B.

As noted above, arranging the drop-off plies 318B such that the tips 320of the drop-off plies 318B are staggered relative to each other canadditionally or alternatively help to reduce (or may prevent) ply kinksand/or wrinkles, reduce (or may prevent) resin pockets, and/or increase(or may maximize) interlaminar strength. As an example, in FIG. 3, therespective positions of the tips 320 of the drop-off plies 318B can bestaggered from the first end 310A to the second end 310B. By“staggered”, it is meant that the tips 320 of the drop-off plies 318Bare each at a respective distance from the second end 310B, and therespective distances between the tips 320 and the second end 310B areall different from each other (i.e., the tips of no two drop-off pliesare equidistant from the second end 310B). Staggering the tips 320 ofthe drop-off plies 318B can help to mitigate some or all of thechallenges associated with a clustered arrangement of drop-off pliesdescribed above.

Also, as noted above, spacing the tips 320 relative to each other by atleast one threshold distance can additionally or alternatively help toreduce (or may prevent) ply kinks and/or wrinkles, reduce (or mayprevent) resin pockets, and/or increase (or may maximize) interlaminarstrength. In an example, for each drop-off ply 318B, a distance 328between the tip 320 of the drop-off ply 318B and the tip 320 of anadjacent one of the drop-off plies 318B can be at least ten timesgreater than the ply thickness 326 of the drop-off ply 318B. In thisexample, for each drop-off ply 318B, the adjacent one of the drop-offplies 318B is adjacent to the drop-off ply 318B in a dimension extendingbetween the first outer surface 314 and the second outer surface 316.For instance, as described above, two of the drop-off plies 318B areadjacent to each other only if there is not another one of the drop-offplies 318B between the two of the drop-off plies 318B in the dimensionextending between the first outer surface 314 and the second outersurface 316. Thus, for example, the ply 318 _(i=7) is adjacent to theply 318 _(i=5) and the ply 318 _(i=9), and non-adjacent to the otherdrop-off plies 318B (i.e., plies 218 _(i=11, 13, 16, 18, 20, 22, 24)).

A representative one of the distances 328 is depicted in FIG. 3 betweenthe tips 320 of the ply 318 _(i=7) and the ply 318 _(i=5), which areadjacent to each other. As shown in FIG. 3, the distance 328 between thetip 320 of the ply 318 _(i=7) and the tip of the ply 318 _(i=5) is atleast ten times greater than the ply thickness 326 of the ply 318_(i=7). Similarly, in FIG. 3, the tips 320 of the other adjacent ones ofthe drop-off plies 318B are separated by respective distances 328 thatare at least ten times greater than the ply thickness 326. As describedabove, arranging the drop-off plies 318B such that the tips 320 ofadjacent ones of the drop-off plies 318B are separated by the distance328 of at least ten times the ply thickness 326 can help to reduce (ormay prevent) ply kinks and/or wrinkles, reduce (or may prevent) resinpockets, and/or increase (or may maximize) interlaminar strength.

Additionally or alternatively, for example, a distance 330 betweennon-adjacent ones of the drop-off plies 318B can be at least three timesgreater than the ply thickness 326 of each drop-off ply 318B. Arepresentative one of the distances 330 is depicted in FIG. 3 betweenthe tips 320 of the ply 318 _(i=7) and the ply 318 _(i=22), which arenon-adjacent to each other (e.g., because the plies 318_(i=9, 11, 13, 16, 18, 20) are between the ply 318 _(i=7) and the ply318 _(i=22)). As shown in FIG. 3, the distance 330 between the tip 320of the ply 318 _(i=7) and the tip of the ply 318 _(i=22) is at leastthree times greater than the ply thickness 326 of the ply 318 _(i=7).Similarly, the tips 320 of the other non-adjacent ones of the drop-offplies 318B are separated by respective distances 330 that are at leastthree times greater than the ply thickness 326. As described above,arranging the drop-off plies 318B such that the tips 320 of non-adjacentones of the drop-off plies 318B are separated by the distance 328 of atleast three times the ply thickness 326 can help to reduce (or mayprevent) ply kinks and/or wrinkles, reduce (or may prevent) resinpockets, and/or increase (or may maximize) interlaminar strength.

In FIG. 3, the ply thickness 326 is the same for all of the plies 318_(i). However, in another example, one or more of the plies 318 _(i) canhave a different ply thickness than another one of the plies 318 _(i).In some implementations, providing the plies 318 _(i) with different plythicknesses can help to provide relatively greater flexibility forachieving fabrication quality objectives.

Additionally, in FIG. 3, the tips 320 of the drop-off plies 318B allhave the tapered shape. However, in another example, one or more of thetips 320 of the drop-off plies 318B can have the blunt-end shape of thetips 120 shown in FIG. 1. Although the tapered shape can be beneficialfor at least the reasons described above, a composite structureincluding the drop-off plies 318B having the tips 120 with the blunt-endshape in a pattern having one or more of the characteristics describedabove with respect to FIG. 3 can provide improvements over the compositestructure 100 shown in FIG. 1.

In FIGS. 1-3, the composite structures 100, 200, 300 are shown having ashape that curves between the first end 110A, 210A, 310A and the secondend 110B, 210B, 310B. However, in other examples, the compositestructures 100, 200, 300 can have a different shape such as, forexample, a planar shape, a scalloped shape, a corrugated shape, auniform shape, a non-uniform shape, a polygonal shape, and/or anon-polygonal shape.

In some examples, the first end 110A, 210A, 310A and/or the second end110B, 210B, 310B can form external surfaces of the composite structure100, 200, 300. However, in other examples, the first end 110A, 210A,310A and/or the second end 110B, 210B, 310B can be respective interfaceswith other segments of a larger composite structure. For instance, thecomposite structure 100, 200, 300 shown in FIGS. 1-3 can provide atransition segment of a composite structure for transitioning from onegage to another gage within the composite structure.

Referring to FIG. 4, a simplified block diagram of a composite structure400 having a variable gage is shown, according to another example. Asshown in FIG. 4, the composite structure 400 includes a first segment440, a second segment 442, and a transition segment 444 between thefirst segment 440 and the second segment 442. The first segment 440 hasa first gage 412A and the second segment 442 has a second gage 412B,which is less than the first gage 412A. Although FIG. 4 depicts thecomposite structure 400 having three segments (i.e., the first segment440, a transition segment 444, and a second segment 442), the compositestructure 400 can include a lesser quantity or a greater quantity ofsegments in other examples.

The transition segment 444 can have a variable gage for transitioningfrom between the first gage 412A and the second gage 412B. For example,the transition segment 444 can include one or more continuous plies andone or more drop-off plies, which are configured to transition betweenthe first gage 412A and the second gage 412B as described above withrespect to the composite structures 100, 200, 300 shown in FIGS. 1-3.

For instance, as shown in FIG. 4, the transition segment 444 includes afirst end 410A at the first segment 440 and having the first gage 412A,a second end 410B at the second segment 442 and having a second gage412B, a first outer surface 414 extending from the first end 410A to thesecond end 410B, a second outer surface 416 extending from the first end410A to the second end 410B. The first end 410A can thus provide aninterface between the first segment 440 and the transition segment 444,and the second end 410B can provide an interface between the secondsegment 442 and the transition segment 444.

The transition segment 444 also includes a plurality of plies 418 (i)extending between the first end 410A and the second end 410B and (ii)arranged in a stack between the first outer surface 414 and the secondouter surface 416. As shown in FIG. 4, the plies 418 include a pluralityof continuous plies 418A and at least one drop-off ply 418B. Asdescribed above, each continuous ply 418A extends from the first end410A to the second end 410B, each drop-off ply 418B includes a tip 420,and each drop-off ply 418B extends from the first end 410A to arespective position of the tip 420 of the drop-off ply 418B between thefirst end 410A and the second end 410B. Within examples, the tips 420 ofthe drop-off plies 418B can have a tapered shape (e.g., as shown inFIGS. 2-3) and/or a blunt-end shape (e.g., as shown in FIG. 1).

In some examples, each drop-off ply 418B is sandwiched between and abutsagainst a respective two continuous plies 418A of the plurality ofcontinuous plies 418A. Additionally or alternatively, the tips 420 ofthe drop-off plies 418B can be arranged in a monotonically-outwardpattern (e.g., as shown in FIG. 2), a monotonically-inward pattern(e.g., as shown in FIG. 3), a staggered pattern (e.g., as shown in FIGS.2-3), and/or a substantially mirrored pattern (e.g., as shown in FIGS.2-3) as described above.

For instance, in an implementation in which the tips 420 are arranged inthe monotonically-inward pattern, (i) a first subset of the drop-offplies 418B are between the first outer surface 414 and a central portionof the stack and a second subset of the drop-off plies 418B are betweenthe central portion and the second outer surface 416, (ii) in a firstorder of the first subset of the drop-off plies 418B from the firstouter surface 414 toward the central portion, with each successivedrop-off ply 418B in the first order, a relative distance between thetip 420 of the drop-off ply 418B and the second end 410B decreases, and(iii) in a second order of the second subset of the drop-off plies 418Bfrom the second outer surface 416 toward the central portion, with eachsuccessive drop-off ply 418B in the second order, a relative distancebetween the tip 420 of the drop-off ply 418B and the second end 410Bdecreases.

Additionally, for instance, in an implementation in which the tips 420are arranged in the monotonically-outward pattern, (i) a first subset ofthe drop-off plies 418B are between the first outer surface 414 and acentral portion of the stack and a second subset of the drop-off plies418B are between the central portion and the second outer surface 416,(ii) in a first order of the first subset of the drop-off plies 418Bfrom the central portion toward the first outer surface 414, with eachsuccessive drop-off ply 418B in the first order, a relative distancebetween the tip 420 of the drop-off ply 418B and the second end 410Bdecreases, and (iii) in a second order of the second subset of thedrop-off plies 418B from the central portion toward the second outersurface 416, with each successive drop-off ply 418B in the second order,a relative distance between the tip 420 of the drop-off ply 418B and thesecond end 410B decreases.

Additionally or alternatively, for each drop-off ply 418B, a distancebetween the tip 420 of the drop-off ply 418B and the tip 420 of anadjacent one of the drop-off plies 418B can be at least ten timesgreater than a thickness of the drop-off ply 418B. Additionally oralternatively, a distance between non-adjacent ones of the drop-offplies 418B can be at least three times greater than a thickness of eachdrop-off ply 418B.

Within examples, the composite structures 100, 200, 300, 400 describedabove with respect to FIGS. 1-4 can be used to form a variety ofstructures. As examples, an aircraft, a spacecraft, a rotorcraft, awatercraft, an automobile, a truck, and/or another type of vehicle(e.g., passenger capsules or cargo containers) can include the compositestructures 100, 200, 300, 400 described above. Additionally, forexample, a building, a bridge, a swimming pool, a storage tank, roboticframe structures, energy structures (e.g., wind blades, turbine blades,propulsion blades, and/or solar panels), sporting goods (e.g., bicycleframes, skis, snow boards, surfing boards, paddles), residential houses,office buildings, and/or medical board frames can include the compositestructures 100, 200, 300, 400 described above.

As one example, FIGS. 5A-5B depict composite stringers 550 that caninclude one or more of the composite structures 100, 200, 300, 400described above with respect to FIGS. 1-4. In general, the compositestringers 550 are each an elongate member that can be coupled to one ormore skin panels to help carry and/or transfer a load from the skinpanel to another structure of the aircraft (e.g., a frame, a rib, and/ora spar of the aircraft). In this way, the composite stringers 550 canhelp to prevent buckling under compression or shear loads on the skinpanels, and/or mitigate bending of the skin panels. For these and otherreasons, the aircraft typically includes one or more composite stringers550 in a fuselage, wing assemblies, and/or an empennage of the aircraft.

In general, the composite stringer 550 includes one or more flanges552A-552C and one or more webs 554A-554B. More particularly, in FIGS.5A-5B, the composite stringer 550 includes a skin flange 552A configuredto be coupled to the support structure 556 (e.g., a skin panel of anaircraft), a top flange 552B, and a web 554A extending between the skinflange 552A and the top flange 552B. In FIG. 5, the composite stringer550 is in the form of a hat-shaped stringer. As such, the web 554A canextend from a first side of the top flange 550B, and the compositestringer 550 can further include a second skin flange 552C configured tobe coupled to the support structure 556 and a second web 554B extendingbetween the second skin flange 552C and a second side of the top flange552B.

Within examples, the composite stringer 550 can further include one ormore corner portions, which each provides a transition segment betweentwo other segments of the composite stringer 550 (i.e., between two ofthe skin flange 552A, the web 554A, the top flange 552B, the second web554B, and the second skin flange 552C). For instance, in FIG. 5, thecorner portion(s) of the composite stringer 550 can include (i) a firstcorner portion 558A extending from the skin flange 552A to the web 554A,(ii) an second corner portion 558B extending from the web 554A to thetop flange 552B, (iii) a third corner portion 558C extending from thesecond skin flange 552C to the second web 554B, and/or (iv) a fourthcorner portion 558D extending from the second web 554B to the top flange552B.

Also, in FIG. 5, the top flange 552B has a first gage 512A. The skinflange 552A, the second skin flange 552C, the web 554A, and the secondweb 554B all have a second gage 512B. In this example, the first gage512A is greater than the second gage 512B.

In this arrangement, the second corner portion 558B and the fourthcorner portion 558D can be a composite structure having a variable gage.For instance, the top flange 552B can be a first segment (e.g., thefirst segment 440), the web 554A can be a second segment (e.g., thesecond segment 442 in FIG. 4), and the second corner portion 558B can bea transition segment (e.g., the transition segment 444 in FIG. 4)between the top flange 552B and the web 554A. Similarly, for instance,the top flange 552B can be a first segment (e.g., the first segment440), the second web 554B can be a second segment (e.g., the secondsegment 442 in FIG. 4), and the fourth corner portion 558D can be atransition segment (e.g., the transition segment 444 in FIG. 4) betweenthe top flange 552B and the second web 554B.

In particular, in FIG. 5A, the second corner portion 558B and the fourthcorner portion 558D each include the composite structure 100 shown inFIG. 1. Whereas, in FIG. 5B, the second corner portion 558B and thefourth corner portion 558D each include the composite structure 300shown in FIG. 3. As shown in FIGS. 5A-5B, the composite structure 300 ofFIG. 3, which includes the drop-off plies 318B having the tips 320 withtapered shapes arranged in the monotonically-inward pattern, provides asmoother and relatively more symmetric transition from the first gage512A to the second gage 512B than the composite structure 100 of FIG. 1,which includes the drop-off plies 118B having the tips 120 withblunt-end shapes arranged in a cluster at or near the first outersurface 114.

As described above, FIGS. 5A-5B depict one example of a structure thatcan include the composite structures 100, 200, 300, 400 describedherein. However, as described above, the composite structures 100, 200,300, 400 can be incorporated in structures other than the compositestringers 550 shown in FIGS. 5A-5B.

Referring now to FIG. 6, a flowchart for a process 600 of forming acomposite structure having a variable gage is described according to anexample. As shown in FIG. 6, at block 610, the process 600 includesforming a plurality of continuous plies. At block 612, the process 600includes forming a plurality of drop-off plies. Forming the plurality ofdrop-off plies at block 612 can include forming, for each drop-off ply,a tip of the drop-off ply having a tapered shape at block 612.

At block 616, the process 600 includes positioning the plurality ofcontinuous plies and the plurality of drop-off plies in a stack having afirst end and a second end. The first end has a first gage. The secondend has a second gage, which is less than the first gage. As shown inFIG. 6, positioning the plurality of continuous plies and the pluralityof drop-off plies at block 616 can include positioning the plurality ofcontinuous plies such that each continuous ply extends from the firstend to the second end at block 618. Positioning the plurality ofcontinuous plies and the plurality of drop-off plies at block 616 canalso include positioning the plurality of drop-off plies such that (i)each drop-off ply extends from the first end to a respective position ofthe tip of the drop-off ply between the first end and the second end,and (ii) the plurality of drop-off plies are separated from each otherby at least one of the plurality of continuous plies at block 620.

FIGS. 7-14 depict additional aspects of the process 600 according tofurther examples. As shown in FIG. 7, the process 600 can furtherinclude, after positioning the plurality of continuous plies and theplurality of drop-off plies in the stack at block 616, curing theplurality of continuous plies and the plurality of drop-off plies atblock 622.

As shown in FIG. 8, positioning the plurality of continuous plies andthe plurality of drop-off plies in the stack at block 616 can furtherinclude forming a first outer surface extending from the first end tothe second end at block 624, and forming a second outer surfaceextending from the first end to the second end at block 626. The firstgage and the second gage can be respective thicknesses between the firstouter surface and the second outer surface at the first end and thesecond end, respectively.

As shown in FIG. 9, positioning the plurality of continuous plies andthe plurality of drop-off plies in the stack at block 616 can includepositioning a first subset of the plurality of drop-off plies betweenthe first outer surface and a central portion at block 628. The centralportion (i) is between the first outer surface and the second outersurface and (ii) extends from the first end to the second end. Also, inFIG. 9, positioning the plurality of continuous plies and the pluralityof drop-off plies in the stack at block 616 can include positioning asecond subset of the plurality of drop-off plies between the centralportion and the second outer surface at block 630.

As shown in FIG. 10, positioning the first subset of the plurality ofdrop-off plies at block 628 and positioning the second subset of theplurality of drop-off plies at block 630 can include positioning theplurality of drop-off plies such that the tips of the first subset ofthe plurality of drop-off plies are arranged in a pattern thatsubstantially mirrors a pattern of the tips of the second subset of theplurality of drop-off plies at block 632.

As shown in FIG. 11, positioning the plurality of drop-off plies atblock 620 can include positioning the plurality of drop-off plies suchthat the respective positions of the tips of the plurality of drop-offplies are staggered from the first end to the second end at block 634.

As shown in FIG. 12, positioning the first subset of the plurality ofdrop-off plies at block 628 can include (i) positioning the first subsetof the plurality of drop-off plies in an order from a drop-off plyclosest to the central portion to a drop-off ply closest to the firstouter surface at block 636, and (ii) positioning the first subset of theplurality of drop-off plies such that the pattern of the tips of thefirst subset of the plurality of drop-off plies includes, with eachsuccessive drop-off ply in the order, a relative distance between thetip of the drop-off ply and the second end decreases at block 638.

Also, as shown in FIG. 12, positioning the second subset of theplurality of drop-off plies at block 630 can include (i) positioning thesecond subset of the plurality of drop-off plies includes positioningthe second subset of the plurality of drop-off plies in an order from adrop-off ply closest to the central portion to a drop-off ply closest tothe second outer surface at block 640, and (ii) positioning the secondsubset of the plurality of drop-off plies such that the pattern of thetips of the second subset of the plurality of drop-off plies includes,with each successive drop-off ply in the order, a relative distancebetween the tip of the drop-off ply and the second end decreases atblock 642.

As shown in FIG. 13, positioning the plurality of drop-off plies atblock 620 can include positioning the plurality of drop-off plies suchthat, for each drop-off ply, a distance between the tip of the drop-offply and the tip of an adjacent one of the plurality of drop-off plies isat least ten times greater than a thickness of the drop-off ply at block644. For each drop-off ply, the adjacent one of the plurality ofdrop-off plies is adjacent to the drop-off ply in a dimension extendingbetween the first outer surface and the second outer surface.

As shown in FIG. 14, positioning the plurality of drop-off plies atblock 620 can include positioning the plurality of drop-off plies suchthat a distance between non-adjacent ones of the plurality of drop-offplies is at least three times greater than a thickness of each drop-offply at block 646.

Referring now to FIG. 15, a flowchart for a process 1500 of forming acomposite structure having a variable gage is described according to anexample. As shown in FIG. 15, at block 1510, the process 1500 includesforming a plurality of continuous plies. At block 1512, the process 1500includes forming a plurality of drop-off plies. Forming the plurality ofdrop-off plies at block 1512 can include forming, for each drop-off ply,a tip of the drop-off ply having a tapered shape at block 1514.

At block 1516, the process 1500 can include positioning the plurality ofcontinuous plies and the plurality of drop-off plies in a stack having(i) a first end, (ii) a second end, (iii) a first outer surfaceextending from the first end to the second end, and (iv) a second outersurface extending from the first end to the second end. The first endhas a first gage. The second end has a second gage, which is less thanthe first gage.

In FIG. 15, positioning the plurality of continuous plies and theplurality of drop-off plies at block 1516 can include positioning theplurality of continuous plies such that each continuous ply extends fromthe first end to the second end at block 1518. Additionally, positioningthe plurality of continuous plies and the plurality of drop-off plies atblock 1516 can also include positioning the plurality of drop-off pliessuch that each drop-off ply extends from the first end to a respectiveposition of the tip of the drop-off ply between the first end and thesecond end at block 1520. A first subset of the plurality of drop-offplies are between the first outer surface and a central portion of thestack and a second subset of the plurality of drop-off plies are betweenthe central portion and the second outer surface.

FIGS. 16-21 depict additional aspects of the process 1500 according tofurther examples. As shown in FIG. 16, positioning the plurality ofcontinuous plies and the plurality of drop-off plies in the stack atblock 1516 can further include, at block 1522, arranging the pluralityof drop-off plies in a monotonically-inward pattern including (i) in afirst order of the first subset of the plurality of drop-off plies fromthe first outer surface toward the central portion, with each successivedrop-off ply in the first order, a relative distance between the tip ofthe drop-off ply and the second end decreases, and (ii) in a secondorder of the second subset of the plurality of drop-off plies from thesecond outer surface toward the central portion, with each successivedrop-off ply in the second order, a relative distance between the tip ofthe drop-off ply and the second end decreases.

As shown in FIG. 17, after positioning the plurality of continuous pliesand the plurality of drop-off plies in the stack at block 1516, theprocess 1500 can include curing the plurality of continuous plies andthe plurality of drop-off plies at block 1524.

As shown in FIG. 18, positioning the plurality of continuous plies andthe plurality of drop-off plies at block 1516 can include positioningthe plurality of continuous plies and the plurality of drop-off pliessuch that the plurality of drop-off plies are separated from each otherby at least one of the plurality of continuous plies at block 1526.

As shown in FIG. 19, positioning the plurality of drop-off plies atblock 1520 can include positioning the plurality of drop-off plies suchthat the respective positions of the tips of the plurality of drop-offplies are staggered from the first end to the second end at block 1528.

As shown in FIG. 20, positioning the plurality of drop-off plies atblock 1520 can include positioning the plurality of drop-off plies suchthat, for each drop-off ply, a distance between the tip of the drop-offply and the tip of an adjacent one of the plurality of drop-off plies isat least ten times greater than a thickness of the drop-off ply at block1530. For each drop-off ply, the adjacent one of the plurality ofdrop-off plies is adjacent to the drop-off ply in a dimension extendingbetween the first outer surface and the second outer surface.

As shown in FIG. 21, positioning the plurality of drop-off plies atblock 1520 can include positioning the plurality of drop-off plies suchthat a distance between non-adjacent ones of the plurality of drop-offplies is at least three times greater than a thickness of each drop-offply at block 1532.

One or more of the blocks shown in FIGS. 6-21 may represent a module, asegment, or a portion of program code, which includes one or moreinstructions executable by a processor for implementing specific logicalfunctions or steps in the process. The program code may be stored on anytype of computer readable medium or data storage, for example, such as astorage device including a disk or hard drive. Further, the program codecan be encoded on a computer-readable storage media in amachine-readable format, or on other non-transitory media or articles ofmanufacture. The computer readable medium may include non-transitorycomputer readable medium or memory, for example, such ascomputer-readable media that stores data for short periods of time likeregister memory, processor cache and Random Access Memory (RAM). Thecomputer readable medium may also include non-transitory media, such assecondary or persistent long term storage, like read only memory (ROM),optical or magnetic disks, compact-disc read only memory (CD-ROM), forexample. The computer readable media may also be any other volatile ornon-volatile storage systems. The computer readable medium may beconsidered a tangible computer readable storage medium, for example.

In some instances, components of the devices and/or systems describedherein may be configured to perform the functions such that thecomponents are actually configured and structured (with hardware and/orsoftware) to enable such performance. Example configurations theninclude one or more processors executing instructions to cause thesystem to perform the functions. Similarly, components of the devicesand/or systems may be configured so as to be arranged or adapted to,capable of, or suited for performing the functions, such as whenoperated in a specific manner.

Further, the disclosure comprises examples according to the followingclauses:

Clause 1: A composite structure having a variable gage including a firstend having a first gage, and a second end having a second gage, which isless than the first gage. The composite structure also includes aplurality of continuous plies and a plurality of drop-off plies. Eachcontinuous ply extends from the first end to the second end. Eachdrop-off ply includes a tip having a tapered shape. Each drop-off plyextends from the first end to a respective position of the tip of thedrop-off ply between the first end and the second end. The plurality ofdrop-off plies are separated from each other by at least one of theplurality of continuous plies.

Clause 2: The composite structure of Clause 1, further including a firstouter surface extending from the first end to the second end, and asecond outer surface extending from the first end to the second end. Theplurality of continuous plies and the plurality of drop-off plies arearranged in a stack between the first outer surface and the second outersurface. The first gage and the second gage are respective thicknessesbetween the first outer surface and the second outer surface at thefirst end and the second end, respectively.

Clause 3: The composite structure of Clause 2, wherein a first subset ofthe plurality of drop-off plies are between the first outer surface anda central portion. The central portion (i) is between the first outersurface and the second outer surface and (ii) extends from the first endto the second end. A second subset of the plurality of drop-off pliesare between the central portion and the second outer surface. The tipsof the first subset of the plurality of drop-off plies are arranged in apattern that substantially mirrors a pattern of the tips of the secondsubset of the plurality of drop-off plies.

Clause 4: The composite structure of Clause 3, wherein the centralportion includes a single drop-off ply of the plurality of drop-offplies.

Clause 5: The composite structure of Clause 3, wherein the centralportion includes two drop-off plies of the plurality of drop-off pliesand at least one continuous ply of the plurality of continuous pliesbetween the two drop-off plies.

Clause 6: The composite structure of any one of Clause 1-5, wherein therespective positions of the tips of the plurality of drop-off plies arestaggered from the first end to the second end.

Clause 7: The composite structure of Clause 6, wherein the first subsetof the plurality of drop-off plies are in an order from a drop-off plyclosest to the central portion to a drop-off ply closest to the firstouter surface. The pattern of the tips of the first subset of theplurality of drop-off plies includes, with each successive drop-off plyin the order, a relative distance between the tip of the drop-off plyand the second end decreases. The second subset of the plurality ofdrop-off plies are in an order from a drop-off ply closest to thecentral portion to a drop-off ply closest to the second outer surface.The pattern of the tips of the second subset of the plurality ofdrop-off plies includes, with each successive drop-off ply in the order,a relative distance between the tip of the drop-off ply and the secondend decreases.

Clause 8: The composite structure of any one of Clause 2-7, wherein, foreach drop-off ply, a distance between the tip of the drop-off ply andthe tip of an adjacent one of the plurality of drop-off plies is atleast ten times greater than a thickness of the drop-off ply. For eachdrop-off ply, the adjacent one of the plurality of drop-off plies isadjacent to the drop-off ply in a dimension extending between the firstouter surface and the second outer surface.

Clause 9: The composite structure of any one of Clause 1-8, wherein, adistance between non-adjacent ones of the plurality of drop-off plies isat least three times greater than a thickness of each drop-off ply.

Clause 10: A method of forming a composite structure having a variablegage includes forming a plurality of continuous plies and forming aplurality of drop-off plies. Forming the plurality of drop-off pliesincludes forming, for each drop-off ply, a tip of the drop-off plyhaving a tapered shape. The method also includes positioning theplurality of continuous plies and the plurality of drop-off plies in astack having a first end and a second end. The first end has a firstgage. The second end has a second gage, which is less than the firstgage. Positioning the plurality of continuous plies and the plurality ofdrop-off plies includes (a) positioning the plurality of continuousplies such that each continuous ply extends from the first end to thesecond end, and (b) positioning the plurality of drop-off plies suchthat (i) each drop-off ply extends from the first end to a respectiveposition of the tip of the drop-off ply between the first end and thesecond end, and (ii) the plurality of drop-off plies are separated fromeach other by at least one of the plurality of continuous plies.

Clause 11: The method of Clause 10, further including, after positioningthe plurality of continuous plies and the plurality of drop-off plies inthe stack, curing the plurality of continuous plies and the plurality ofdrop-off plies.

Clause 12: The method of any one of Clauses 10-11, wherein positioningthe plurality of continuous plies and the plurality of drop-off plies inthe stack further includes forming a first outer surface extending fromthe first end to the second end, and forming a second outer surfaceextending from the first end to the second end. The first gage and thesecond gage are respective thicknesses between the first outer surfaceand the second outer surface at the first end and the second end,respectively.

Clause 13: The method of Clause 12, wherein positioning the plurality ofcontinuous plies and the plurality of drop-off plies in the stackincludes positioning a first subset of the plurality of drop-off pliesbetween the first outer surface and a central portion, wherein thecentral portion (i) is between the first outer surface and the secondouter surface and (ii) extends from the first end to the second end.Positioning the plurality of continuous plies and the plurality ofdrop-off plies in the stack also includes positioning a second subset ofthe plurality of drop-off plies between the central portion and thesecond outer surface. Positioning the first subset of the plurality ofdrop-off plies and positioning the second subset of the plurality ofdrop-off plies includes positioning the plurality of drop-off plies suchthat the tips of the first subset of the plurality of drop-off plies arearranged in a pattern that substantially mirrors a pattern of the tipsof the second subset of the plurality of drop-off plies.

Clause 14: The method of Clause 13, wherein the central portion includesa single drop-off ply of the plurality of drop-off plies.

Clause 15: The method of Clause 13, wherein the central portion includestwo drop-off plies of the plurality of drop-off plies and at least onecontinuous ply of the plurality of continuous plies between the twodrop-off plies.

Clause 16: The method of any one of Clauses 10-15, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that the respective positions of the tips of theplurality of drop-off plies are staggered from the first end to thesecond end.

Clause 17: The method of Clause 16, wherein positioning the first subsetof the plurality of drop-off plies includes: (i) positioning the firstsubset of the plurality of drop-off plies in an order from a drop-offply closest to the central portion to a drop-off ply closest to thefirst outer surface, and (ii) positioning the first subset of theplurality of drop-off plies such that the pattern of the tips of thefirst subset of the plurality of drop-off plies includes, with eachsuccessive drop-off ply in the order, a relative distance between thetip of the drop-off ply and the second end decreases. Positioning thesecond subset of the plurality of drop-off plies includes: (a)positioning the second subset of the plurality of drop-off pliesincludes positioning the second subset of the plurality of drop-offplies in an order from a drop-off ply closest to the central portion toa drop-off ply closest to the second outer surface, and (b) positioningthe second subset of the plurality of drop-off plies such that thepattern of the tips of the second subset of the plurality of drop-offplies includes, with each successive drop-off ply in the order, arelative distance between the tip of the drop-off ply and the second enddecreases.

Clause 18: The method of any one of Clauses 10-17, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that, for each drop-off ply, a distance between thetip of the drop-off ply and the tip of an adjacent one of the pluralityof drop-off plies is at least ten times greater than a thickness of thedrop-off ply. For each drop-off ply, the adjacent one of the pluralityof drop-off plies is adjacent to the drop-off ply in a dimensionextending between the first outer surface and the second outer surface.

Clause 19: The method of any one of Clauses 10-18, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that a distance between non-adjacent ones of theplurality of drop-off plies is at least three times greater than athickness of each drop-off ply.

Clause 20: A composite structure having a variable gage. The compositestructure includes a first segment having a first gage and a secondsegment having a second gage, which is less than the first gage. Thecomposite structure also includes a transition segment between the firstsegment and the second segment. The transition segment includes a firstend at the first segment and having the first gage, a second end at thesecond segment and having a second gage, a first outer surface extendingfrom the first end to the second end, a second outer surface extendingfrom the first end to the second end, and a plurality of plies (i)extending between the first end and the second end and (ii) arranged ina stack between the first outer surface and the second outer surface.The plurality of plies include (a) a plurality of continuous plies,wherein each continuous ply extends from the first end to the secondend, and (b) at least one drop-off ply, wherein each drop-off plycomprises a tip having a tapered shape, wherein each drop-off plyextends from the first end to a respective position of the tip of thedrop-off ply between the first end and the second end. Each drop-off plyis sandwiched between and abuts against a respective two continuousplies of the plurality of continuous plies.

Clause 21: A composite structure having a variable gage including afirst end having a first gage, and a second end having a second gage,which is less than the first gage. The composite structure also includesa first outer surface extending from the first end to the second end, asecond outer surface extending from the first end to the second end, anda plurality of plies (i) extending between the first end and the secondend and (ii) arranged in a stack between the first outer surface and thesecond outer surface. The plurality of plies include a plurality ofcontinuous plies and a plurality of drop-off plies. Each continuous plyextends from the first end to the second end. Each drop-off ply includesa tip having a tapered shape. Each drop-off ply extends from the firstend to a respective position of the tip of the drop-off ply between thefirst end and the second end. A first subset of the plurality ofdrop-off plies are between the first outer surface and a central portionof the stack, and a second subset of the plurality of drop-off plies arebetween the central portion and the second outer surface. The tips ofthe plurality of drop-off plies are arranged in a monotonically-inwardpattern including: (i) in a first order of the first subset of theplurality of drop-off plies from the first outer surface toward thecentral portion, with each successive drop-off ply in the first order, arelative distance between the tip of the drop-off ply and the second enddecreases, and (ii) in a second order of the second subset of theplurality of drop-off plies from the second outer surface toward thecentral portion, with each successive drop-off ply in the second order,a relative distance between the tip of the drop-off ply and the secondend decreases.

Clause 22: The composite structure of Clause 21, wherein the pluralityof drop-off plies are separated from each other by at least one of theplurality of continuous plies.

Clause 23: The composite structure of any one of Clauses 21-22, whereinthe first gage and the second gage are respective thicknesses betweenthe first outer surface and the second outer surface at the first endand the second end, respectively.

Clause 24: The composite structure of any one of Clauses 21-23, whereinthe central portion consists of at least one continuous ply of theplurality of continuous plies.

Clause 25: The composite structure of any one of Clauses 21-24, whereinthe respective positions of the tips of the plurality of drop-off pliesare staggered from the first end to the second end.

Clause 26: The composite structure of Clauses 21-25, wherein themonotonically-inward pattern further includes, along a direction fromthe first end to the second end, the tips of the first subset of theplurality of drop-off plies alternating with the tips of the secondsubset of the plurality of drop-off plies.

Clause 27: The composite structure of any one of Clauses 21-26, whereinthe plurality of drop-off plies are arranged in a plurality of pairs ofdrop-off plies. Each pair of drop-off plies includes a respective onedrop-off ply of the first subset and a respective one drop-off ply ofthe second subset. For each pair of drop-off plies, the respective onedrop-off ply of the first subset and the respective one drop-off ply ofthe second subset are substantially equidistant from the central portionin a dimension between the first outer surface and the second outersurface.

Clause 28: The composite structure of any one of Clauses 21-27, whereineach drop-off ply has a ply angle, relative to a longitudinal axis ofthe composite structure, which is between approximately −30 degrees and+30 degrees.

Clause 29: The composite structure of Clause 28, wherein, for each pair,the ply angle is approximately the same for the plurality of drop-offplies of the pair.

Clause 30: The composite structure of any one of Clauses 21-29, wherein,for each drop-off ply, a distance between the tip of the drop-off plyand the tip of an adjacent one of the plurality of drop-off plies is atleast ten times greater than a thickness of the drop-off ply. For eachdrop-off ply, the adjacent one of the plurality of drop-off plies isadjacent to the drop-off ply in a dimension extending between the firstouter surface and the second outer surface.

Clause 31: The composite structure of any one of Clauses 21-30, whereina distance between non-adjacent ones of the plurality of drop-off pliesis at least three times greater than a thickness of each drop-off ply.

Clause 32: A method of forming a composite structure having a variablegage including forming a plurality of continuous plies and forming aplurality of drop-off plies. Forming the plurality of drop-off pliesincludes forming, for each drop-off ply, a tip of the drop-off plyhaving a tapered shape. The method also includes positioning theplurality of continuous plies and the plurality of drop-off plies in astack having (i) a first end, (ii) a second end, (iii) a first outersurface extending from the first end to the second end, and (iv) asecond outer surface extending from the first end to the second end. Thefirst end has a first gage and the second end has a second gage, whichis less than the first gage. Positioning the plurality of continuousplies and the plurality of drop-off plies includes positioning theplurality of continuous plies such that each continuous ply extends fromthe first end to the second end, and positioning the plurality ofdrop-off plies such that each drop-off ply extends from the first end toa respective position of the tip of the drop-off ply between the firstend and the second end. A first subset of the plurality of drop-offplies are between the first outer surface and a central portion of thestack, and a second subset of the plurality of drop-off plies arebetween the central portion and the second outer surface. Positioningthe plurality of continuous plies and the plurality of drop-off plies inthe stack further includes arranging the plurality of drop-off plies ina monotonically-inward pattern including: (a) in a first order of thefirst subset of the plurality of drop-off plies from the first outersurface toward the central portion, with each successive drop-off ply inthe first order, a relative distance between the tip of the drop-off plyand the second end decreases, and (b) in a second order of the secondsubset of the plurality of drop-off plies from the second outer surfacetoward the central portion, with each successive drop-off ply in thesecond order, a relative distance between the tip of the drop-off plyand the second end decreases.

Clause 33: The method of Clause 32, further including, after positioningthe plurality of continuous plies and the plurality of drop-off plies inthe stack, curing the plurality of continuous plies and the plurality ofdrop-off plies.

Clause 34: The method of any one of Clauses 32-33, wherein positioningthe plurality of continuous plies and the plurality of drop-off pliesincludes positioning the plurality of continuous plies and the pluralityof drop-off plies such that the plurality of drop-off plies areseparated from each other by at least one of the plurality of continuousplies.

Clause 35: The method of any one of Clauses 32-34, wherein the centralportion consists of at least one continuous ply of the plurality ofcontinuous plies.

Clause 36: The method of any one of Clauses 32-35, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that the respective positions of the tips of theplurality of drop-off plies are staggered from the first end to thesecond end.

Clause 37: The method of any one of Clauses 32-36, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that, for each drop-off ply, a distance between thetip of the drop-off ply and the tip of an adjacent one of the pluralityof drop-off plies is at least ten times greater than a thickness of thedrop-off ply. For each drop-off ply, the adjacent one of the pluralityof drop-off plies is adjacent to the drop-off ply in a dimensionextending between the first outer surface and the second outer surface.

Clause 38: The method of any one of Clauses 32-37, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that a distance between non-adjacent ones of theplurality of drop-off plies is at least three times greater than athickness of each drop-off ply.

Clause 39: A composite structure having a variable gage. The compositestructure includes a first segment having a first gage and a secondsegment having a second gage, which is less than the first gage. Thecomposite structure also includes a transition segment between the firstsegment and the second segment. The transition segment includes a firstend at the first segment and having the first gage, a second end at thesecond segment and having a second gage, a first outer surface extendingfrom the first end to the second end, a second outer surface extendingfrom the first end to the second end, and a plurality of plies (i)extending between the first end and the second end and (ii) arranged ina stack between the first outer surface and the second outer surface.The plurality of plies include a plurality of continuous plies and aplurality of drop-off plies. Each continuous ply extends from the firstend to the second end. Each drop-off ply includes a tip having a taperedshape. Each drop-off ply extends from the first end to a respectiveposition of the tip of the drop-off ply between the first end and thesecond end. A first subset of the plurality of drop-off plies arebetween the first outer surface and a central portion of the stack and asecond subset of the plurality of drop-off plies are between the centralportion and the second outer surface. The tips of the plurality ofdrop-off plies are arranged in a monotonically-inward patterncomprising: (a) in a first order of the first subset of the plurality ofdrop-off plies from the first outer surface toward the central portion,with each successive drop-off ply in the first order, a relativedistance between the tip of the drop-off ply and the second enddecreases, and (b) in a second order of the second subset of theplurality of drop-off plies from the second outer surface toward thecentral portion, with each successive drop-off ply in the second order,a relative distance between the tip of the drop-off ply and the secondend decreases.

Clause 40: The composite structure of Clause 39, wherein the firstsegment is a flange of a composite stringer and the second segment is aweb of the composite stringer.

Clause 41: A composite structure having a variable gage including afirst end having a first gage, and a second end having a second gage,which is less than the first gage. The composite structure also includesa plurality of continuous plies and a plurality of drop-off plies. Eachcontinuous ply extends from the first end to the second end. Eachdrop-off ply includes a tip having a blunt-end shape. Each drop-off plyextends from the first end to a respective position of the tip of thedrop-off ply between the first end and the second end. The plurality ofdrop-off plies are separated from each other by at least one of theplurality of continuous plies.

Clause 42: The composite structure of Clause 41, further including afirst outer surface extending from the first end to the second end, anda second outer surface extending from the first end to the second end.The plurality of continuous plies and the plurality of drop-off pliesare arranged in a stack between the first outer surface and the secondouter surface. The first gage and the second gage are respectivethicknesses between the first outer surface and the second outer surfaceat the first end and the second end, respectively.

Clause 43: The composite structure of Clause 42, wherein a first subsetof the plurality of drop-off plies are between the first outer surfaceand a central portion. The central portion (i) is between the firstouter surface and the second outer surface and (ii) extends from thefirst end to the second end. A second subset of the plurality ofdrop-off plies are between the central portion and the second outersurface. The tips of the first subset of the plurality of drop-off pliesare arranged in a pattern that substantially mirrors a pattern of thetips of the second subset of the plurality of drop-off plies.

Clause 44: The composite structure of Clause 43, wherein the centralportion includes a single drop-off ply of the plurality of drop-offplies.

Clause 45: The composite structure of Clause 43, wherein the centralportion includes two drop-off plies of the plurality of drop-off pliesand at least one continuous ply of the plurality of continuous pliesbetween the two drop-off plies.

Clause 46: The composite structure of any one of Clause 41-45, whereinthe respective positions of the tips of the plurality of drop-off pliesare staggered from the first end to the second end.

Clause 47: The composite structure of Clause 46, wherein the firstsubset of the plurality of drop-off plies are in an order from adrop-off ply closest to the central portion to a drop-off ply closest tothe first outer surface. The pattern of the tips of the first subset ofthe plurality of drop-off plies includes, with each successive drop-offply in the order, a relative distance between the tip of the drop-offply and the second end decreases. The second subset of the plurality ofdrop-off plies are in an order from a drop-off ply closest to thecentral portion to a drop-off ply closest to the second outer surface.The pattern of the tips of the second subset of the plurality ofdrop-off plies includes, with each successive drop-off ply in the order,a relative distance between the tip of the drop-off ply and the secondend decreases.

Clause 48: The composite structure of any one of Clause 42-47, wherein,for each drop-off ply, a distance between the tip of the drop-off plyand the tip of an adjacent one of the plurality of drop-off plies is atleast ten times greater than a thickness of the drop-off ply. For eachdrop-off ply, the adjacent one of the plurality of drop-off plies isadjacent to the drop-off ply in a dimension extending between the firstouter surface and the second outer surface.

Clause 49: The composite structure of any one of Clause 41-48, wherein,a distance between non-adjacent ones of the plurality of drop-off pliesis at least three times greater than a thickness of each drop-off ply.

Clause 50: A method of forming a composite structure having a variablegage includes forming a plurality of continuous plies and forming aplurality of drop-off plies. Forming the plurality of drop-off pliesincludes forming, for each drop-off ply, a tip of the drop-off plyhaving a blunt-end shape. The method also includes positioning theplurality of continuous plies and the plurality of drop-off plies in astack having a first end and a second end. The first end has a firstgage. The second end has a second gage, which is less than the firstgage. Positioning the plurality of continuous plies and the plurality ofdrop-off plies includes (a) positioning the plurality of continuousplies such that each continuous ply extends from the first end to thesecond end, and (b) positioning the plurality of drop-off plies suchthat (i) each drop-off ply extends from the first end to a respectiveposition of the tip of the drop-off ply between the first end and thesecond end, and (ii) the plurality of drop-off plies are separated fromeach other by at least one of the plurality of continuous plies.

Clause 51: The method of Clauses 50, further including, afterpositioning the plurality of continuous plies and the plurality ofdrop-off plies in the stack, curing the plurality of continuous pliesand the plurality of drop-off plies.

Clause 52: The method of any one of Clauses 50-51, wherein positioningthe plurality of continuous plies and the plurality of drop-off plies inthe stack further includes forming a first outer surface extending fromthe first end to the second end, and forming a second outer surfaceextending from the first end to the second end. The first gage and thesecond gage are respective thicknesses between the first outer surfaceand the second outer surface at the first end and the second end,respectively.

Clause 53: The method of Clause 52, wherein positioning the plurality ofcontinuous plies and the plurality of drop-off plies in the stackincludes positioning a first subset of the plurality of drop-off pliesbetween the first outer surface and a central portion, wherein thecentral portion (i) is between the first outer surface and the secondouter surface and (ii) extends from the first end to the second end.Positioning the plurality of continuous plies and the plurality ofdrop-off plies in the stack also includes positioning a second subset ofthe plurality of drop-off plies between the central portion and thesecond outer surface. Positioning the first subset of the plurality ofdrop-off plies and positioning the second subset of the plurality ofdrop-off plies includes positioning the plurality of drop-off plies suchthat the tips of the first subset of the plurality of drop-off plies arearranged in a pattern that substantially mirrors a pattern of the tipsof the second subset of the plurality of drop-off plies.

Clause 54: The method of Clause 53, wherein the central portion includesa single drop-off ply of the plurality of drop-off plies.

Clause 55: The method of Clause 53, wherein the central portion includestwo drop-off plies of the plurality of drop-off plies and at least onecontinuous ply of the plurality of continuous plies between the twodrop-off plies.

Clause 56: The method of any one of Clauses 50-55, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that the respective positions of the tips of theplurality of drop-off plies are staggered from the first end to thesecond end.

Clause 57: The method of Clause 56, wherein positioning the first subsetof the plurality of drop-off plies includes: (i) positioning the firstsubset of the plurality of drop-off plies in an order from a drop-offply closest to the central portion to a drop-off ply closest to thefirst outer surface, and (ii) positioning the first subset of theplurality of drop-off plies such that the pattern of the tips of thefirst subset of the plurality of drop-off plies includes, with eachsuccessive drop-off ply in the order, a relative distance between thetip of the drop-off ply and the second end decreases. Positioning thesecond subset of the plurality of drop-off plies includes: (a)positioning the second subset of the plurality of drop-off pliesincludes positioning the second subset of the plurality of drop-offplies in an order from a drop-off ply closest to the central portion toa drop-off ply closest to the second outer surface, and (b) positioningthe second subset of the plurality of drop-off plies such that thepattern of the tips of the second subset of the plurality of drop-offplies includes, with each successive drop-off ply in the order, arelative distance between the tip of the drop-off ply and the second enddecreases.

Clause 58: The method of any one of Clauses 50-57, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that, for each drop-off ply, a distance between thetip of the drop-off ply and the tip of an adjacent one of the pluralityof drop-off plies is at least ten times greater than a thickness of thedrop-off ply. For each drop-off ply, the adjacent one of the pluralityof drop-off plies is adjacent to the drop-off ply in a dimensionextending between the first outer surface and the second outer surface.

Clause 59: The method of any one of Clauses 50-58, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that a distance between non-adjacent ones of theplurality of drop-off plies is at least three times greater than athickness of each drop-off ply.

Clause 60: A composite structure having a variable gage. The compositestructure includes a first segment having a first gage and a secondsegment having a second gage, which is less than the first gage. Thecomposite structure also includes a transition segment between the firstsegment and the second segment. The transition segment includes a firstend at the first segment and having the first gage, a second end at thesecond segment and having a second gage, a first outer surface extendingfrom the first end to the second end, a second outer surface extendingfrom the first end to the second end, and a plurality of plies (i)extending between the first end and the second end and (ii) arranged ina stack between the first outer surface and the second outer surface.The plurality of plies include (a) a plurality of continuous plies,wherein each continuous ply extends from the first end to the secondend, and (b) at least one drop-off ply, wherein each drop-off plycomprises a tip having a blunt-end shape, wherein each drop-off plyextends from the first end to a respective position of the tip of thedrop-off ply between the first end and the second end. Each drop-off plyis sandwiched between and abuts against a respective two continuousplies of the plurality of continuous plies.

Clause 61: A composite structure having a variable gage including afirst end having a first gage, and a second end having a second gage,which is less than the first gage. The composite structure also includesa first outer surface extending from the first end to the second end, asecond outer surface extending from the first end to the second end, anda plurality of plies (i) extending between the first end and the secondend and (ii) arranged in a stack between the first outer surface and thesecond outer surface. The plurality of plies include a plurality ofcontinuous plies and a plurality of drop-off plies. Each continuous plyextends from the first end to the second end. Each drop-off ply includesa tip having a blunt-end shape. Each drop-off ply extends from the firstend to a respective position of the tip of the drop-off ply between thefirst end and the second end. A first subset of the plurality ofdrop-off plies are between the first outer surface and a central portionof the stack, and a second subset of the plurality of drop-off plies arebetween the central portion and the second outer surface. The tips ofthe plurality of drop-off plies are arranged in a monotonically-inwardpattern including: (i) in a first order of the first subset of theplurality of drop-off plies from the first outer surface toward thecentral portion, with each successive drop-off ply in the first order, arelative distance between the tip of the drop-off ply and the second enddecreases, and (ii) in a second order of the second subset of theplurality of drop-off plies from the second outer surface toward thecentral portion, with each successive drop-off ply in the second order,a relative distance between the tip of the drop-off ply and the secondend decreases.

Clause 62: The composite structure of Clause 61, wherein the pluralityof drop-off plies are separated from each other by at least one of theplurality of continuous plies.

Clause 63: The composite structure of any one of Clauses 61-62, whereinthe first gage and the second gage are respective thicknesses betweenthe first outer surface and the second outer surface at the first endand the second end, respectively.

Clause 64: The composite structure of any one of Clauses 61-63, whereinthe central portion consists of at least one continuous ply of theplurality of continuous plies.

Clause 65: The composite structure of any one of Clauses 61-64, whereinthe respective positions of the tips of the plurality of drop-off pliesare staggered from the first end to the second end.

Clause 66: The composite structure of Clauses 61-65, wherein themonotonically-inward pattern further includes, along a direction fromthe first end to the second end, the tips of the first subset of theplurality of drop-off plies alternating with the tips of the secondsubset of the plurality of drop-off plies.

Clause 67: The composite structure of any one of Clauses 61-66, whereinthe plurality of drop-off plies are arranged in a plurality of pairs ofdrop-off plies. Each pair of drop-off plies includes a respective onedrop-off ply of the first subset and a respective one drop-off ply ofthe second subset. For each pair of drop-off plies, the respective onedrop-off ply of the first subset and the respective one drop-off ply ofthe second subset are substantially equidistant from the central portionin a dimension between the first outer surface and the second outersurface.

Clause 68: The composite structure of any one of Clauses 61-67, whereineach drop-off ply has a ply angle, relative to a longitudinal axis ofthe composite structure, which is between approximately −30 degrees and+30 degrees.

Clause 69: The composite structure of Clause 68, wherein, for each pair,the ply angle is approximately the same for the plurality of drop-offplies of the pair.

Clause 70: The composite structure of any one of Clauses 61-69, wherein,for each drop-off ply, a distance between the tip of the drop-off plyand the tip of an adjacent one of the plurality of drop-off plies is atleast ten times greater than a thickness of the drop-off ply. For eachdrop-off ply, the adjacent one of the plurality of drop-off plies isadjacent to the drop-off ply in a dimension extending between the firstouter surface and the second outer surface.

Clause 71: The composite structure of any one of Clauses 61-70, whereina distance between non-adjacent ones of the plurality of drop-off pliesis at least three times greater than a thickness of each drop-off ply.

Clause 72: A method of forming a composite structure having a variablegage including forming a plurality of continuous plies and forming aplurality of drop-off plies. Forming the plurality of drop-off pliesincludes forming, for each drop-off ply, a tip of the drop-off plyhaving a blunt-end shape. The method also includes positioning theplurality of continuous plies and the plurality of drop-off plies in astack having (i) a first end, (ii) a second end, (iii) a first outersurface extending from the first end to the second end, and (iv) asecond outer surface extending from the first end to the second end. Thefirst end has a first gage and the second end has a second gage, whichis less than the first gage. Positioning the plurality of continuousplies and the plurality of drop-off plies includes positioning theplurality of continuous plies such that each continuous ply extends fromthe first end to the second end, and positioning the plurality ofdrop-off plies such that each drop-off ply extends from the first end toa respective position of the tip of the drop-off ply between the firstend and the second end. A first subset of the plurality of drop-offplies are between the first outer surface and a central portion of thestack, and a second subset of the plurality of drop-off plies arebetween the central portion and the second outer surface. Positioningthe plurality of continuous plies and the plurality of drop-off plies inthe stack further includes arranging the plurality of drop-off plies ina monotonically-inward pattern including: (a) in a first order of thefirst subset of the plurality of drop-off plies from the first outersurface toward the central portion, with each successive drop-off ply inthe first order, a relative distance between the tip of the drop-off plyand the second end decreases, and (b) in a second order of the secondsubset of the plurality of drop-off plies from the second outer surfacetoward the central portion, with each successive drop-off ply in thesecond order, a relative distance between the tip of the drop-off plyand the second end decreases.

Clause 73: The method of Clause 72, further including, after positioningthe plurality of continuous plies and the plurality of drop-off plies inthe stack, curing the plurality of continuous plies and the plurality ofdrop-off plies.

Clause 74: The method of any one of Clauses 72-73, wherein positioningthe plurality of continuous plies and the plurality of drop-off pliesincludes positioning the plurality of continuous plies and the pluralityof drop-off plies such that the plurality of drop-off plies areseparated from each other by at least one of the plurality of continuousplies.

Clause 75: The method of any one of Clauses 72-74, wherein the centralportion consists of at least one continuous ply of the plurality ofcontinuous plies.

Clause 76: The method of any one of Clauses 72-75, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that the respective positions of the tips of theplurality of drop-off plies are staggered from the first end to thesecond end.

Clause 77: The method of any one of Clauses 72-76, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that, for each drop-off ply, a distance between thetip of the drop-off ply and the tip of an adjacent one of the pluralityof drop-off plies is at least ten times greater than a thickness of thedrop-off ply. For each drop-off ply, the adjacent one of the pluralityof drop-off plies is adjacent to the drop-off ply in a dimensionextending between the first outer surface and the second outer surface.

Clause 78: The method of any one of Clauses 72-77, wherein positioningthe plurality of drop-off plies includes positioning the plurality ofdrop-off plies such that a distance between non-adjacent ones of theplurality of drop-off plies is at least three times greater than athickness of each drop-off ply.

Clause 79: A composite structure having a variable gage. The compositestructure includes a first segment having a first gage and a secondsegment having a second gage, which is less than the first gage. Thecomposite structure also includes a transition segment between the firstsegment and the second segment. The transition segment includes a firstend at the first segment and having the first gage, a second end at thesecond segment and having a second gage, a first outer surface extendingfrom the first end to the second end, a second outer surface extendingfrom the first end to the second end, and a plurality of plies (i)extending between the first end and the second end and (ii) arranged ina stack between the first outer surface and the second outer surface.The plurality of plies include a plurality of continuous plies and aplurality of drop-off plies. Each continuous ply extends from the firstend to the second end. Each drop-off ply includes a tip having ablunt-end shape. Each drop-off ply extends from the first end to arespective position of the tip of the drop-off ply between the first endand the second end. A first subset of the plurality of drop-off pliesare between the first outer surface and a central portion of the stackand a second subset of the plurality of drop-off plies are between thecentral portion and the second outer surface. The tips of the pluralityof drop-off plies are arranged in a monotonically-inward patterncomprising: (a) in a first order of the first subset of the plurality ofdrop-off plies from the first outer surface toward the central portion,with each successive drop-off ply in the first order, a relativedistance between the tip of the drop-off ply and the second enddecreases, and (b) in a second order of the second subset of theplurality of drop-off plies from the second outer surface toward thecentral portion, with each successive drop-off ply in the second order,a relative distance between the tip of the drop-off ply and the secondend decreases.

Clause 80: The composite structure of Clause 79, wherein the firstsegment is a flange of a composite stringer and the second segment is aweb of the composite stringer.

The description of the different advantageous arrangements has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the examples in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different advantageous examplesmay describe different advantages as compared to other advantageousexamples. The example or examples selected are chosen and described inorder to explain the principles of the examples, the practicalapplication, and to enable others of ordinary skill in the art tounderstand the disclosure for various examples with variousmodifications as are suited to the particular use contemplated.

What is claimed is:
 1. A composite structure having a variable gage,comprising: a first end having a first gage; a second end having asecond gage, which is less than the first gage; a first outer surfaceextending from the first end to the second end; a second outer surfaceextending from the first end to the second end; and a plurality of plies(i) extending between the first end and the second end and (ii) arrangedin a stack between the first outer surface and the second outer surface,wherein the plurality of plies comprise: a plurality of continuousplies, wherein each continuous ply extends from the first end to thesecond end; and a plurality of drop-off plies, wherein each drop-off plycomprises a tip having a blunt-end shape, wherein each drop-off plyextends from the first end to a respective position of the tip of thedrop-off ply between the first end and the second end, wherein a firstsubset of the plurality of drop-off plies are between the first outersurface and a central portion of the stack and a second subset of theplurality of drop-off plies are between the central portion and thesecond outer surface, wherein the tips of the plurality of drop-offplies are arranged in a monotonically-inward pattern comprising: (i) ina first order of the first subset of the plurality of drop-off pliesfrom the first outer surface toward the central portion, with eachsuccessive drop-off ply in the first order, a relative distance betweenthe tip of the drop-off ply and the second end decreases, and (ii) in asecond order of the second subset of the plurality of drop-off pliesfrom the second outer surface toward the central portion, with eachsuccessive drop-off ply in the second order, a relative distance betweenthe tip of the drop-off ply and the second end decreases, wherein thefirst gage and the second gage are respective thicknesses between thefirst outer surface and the second outer surface at the first end andthe second end, respectively, wherein the respective positions of thetips of the plurality of drop-off plies of the first subset arestaggered with the respective positions of the tips of the plurality ofdrop-off plies of the second subset from the first end to the secondend, wherein, for each drop-off ply, a first distance between the tip ofthe drop-off ply and the tip of an adjacent one of the plurality ofdrop-off plies is at least ten times greater than a thickness of thedrop-off ply, wherein the first distance is measured along the first endto the second end, wherein, for each drop-off ply, the adjacent one ofthe plurality of drop-off plies is adjacent to the drop-off ply in adimension extending between the first outer surface and the second outersurface, wherein a second distance between the tips of non-adjacent onesof the plurality of drop-off plies is at least three times greater thana thickness of each drop-off ply, and wherein the second distance ismeasured along the first end to the second end.
 2. The compositestructure of claim 1, wherein the plurality of drop-off plies areseparated from each other by at least one of the plurality of continuousplies.
 3. The composite structure of claim 1, wherein the centralportion consists of at least one continuous ply of the plurality ofcontinuous plies.
 4. The composite structure of claim 1, wherein themonotonically-inward pattern further comprises, along a direction fromthe first end to the second end, the tips of the first subset of theplurality of drop-off plies alternating with the tips of the secondsubset of the plurality of drop-off plies.
 5. The composite structure ofclaim 1, wherein the plurality of drop-off plies are arranged in aplurality of pairs of drop-off plies, wherein each pair of drop-offplies comprises a respective one drop-off ply of the first subset and arespective one drop-off ply of the second subset, and wherein, for eachpair of drop-off plies, the respective one drop-off ply of the firstsubset and the respective one drop-off ply of the second subset aresubstantially equidistant from the central portion in a dimensionbetween the first outer surface and the second outer surface.
 6. Thecomposite structure of claim 5, wherein each drop-off ply has a plyangle, relative to a longitudinal axis of the composite structure, whichis between approximately −30 degrees and +30 degrees.
 7. The compositestructure of claim 6, wherein, for each pair, the ply angle isapproximately the same for the plurality of drop-off plies of the pair.8. The composite structure of claim 1, wherein the central portioncomprises a single drop-off ply of the plurality of drop-off plies.
 9. Amethod of forming a composite structure having a variable gage,comprising: forming a plurality of continuous plies; forming a pluralityof drop-off plies, wherein forming the plurality of drop-off pliescomprises forming, for each drop-off ply, a tip of the drop-off plyhaving a blunt-end shape; and positioning the plurality of continuousplies and the plurality of drop-off plies in a stack having (i) a firstend, (ii) a second end, (iii) a first outer surface extending from thefirst end to the second end, and (iv) a second outer surface extendingfrom the first end to the second end, wherein the first end has a firstgage, wherein the second end has a second gage, which is less than thefirst gage, wherein the first gage and the second gage are respectivethicknesses between the first outer surface and the second outer surfaceat the first end and the second end, respectively, and whereinpositioning the plurality of continuous plies and the plurality ofdrop-off plies comprises: positioning the plurality of continuous pliessuch that each continuous ply extends from the first end to the secondend, and positioning the plurality of drop-off plies such that eachdrop-off ply extends from the first end to a respective position of thetip of the drop-off ply between the first end and the second end,wherein a first subset of the plurality of drop-off plies are betweenthe first outer surface and a central portion of the stack and a secondsubset of the plurality of drop-off plies are between the centralportion and the second outer surface, wherein positioning the pluralityof continuous plies and the plurality of drop-off plies in the stackfurther comprises arranging the plurality of drop-off plies in amonotonically-inward pattern comprising: (i) in a first order of thefirst subset of the plurality of drop-off plies from the first outersurface toward the central portion, with each successive drop-off ply inthe first order, a relative distance between the tip of the drop-off plyand the second end decreases, and (ii) in a second order of the secondsubset of the plurality of drop-off plies from the second outer surfacetoward the central portion, with each successive drop-off ply in thesecond order, a relative distance between the tip of the drop-off plyand the second end decreases, wherein positioning the plurality ofdrop-off plies comprises positioning the plurality of drop-off pliessuch that the respective positions of the tips of the plurality ofdrop-off plies of the first subset are staggered with the respectivepositions of the tips of the plurality of drop-off plies of the secondsubset from the first end to the second end, wherein positioning theplurality of drop-off plies comprises positioning the plurality ofdrop-off plies such that, for each drop-off ply, a first distancebetween the tip of the drop-off ply and the tip of an adjacent one ofthe plurality of drop-off plies is at least ten times greater than athickness of the drop-off ply, wherein the first distance is measuredalong the first end to the second end, wherein, for each drop-off ply,the adjacent one of the plurality of drop-off plies is adjacent to thedrop-off ply in a dimension extending between the first outer surfaceand the second outer surface, wherein positioning the plurality ofdrop-off plies comprises positioning the plurality of drop-off pliessuch that a second distance between the tips of non-adjacent ones of theplurality of drop-off plies is at least three times greater than athickness of each drop-off ply, and wherein the second distance ismeasured along the first end to the second end.
 10. The method of claim9, further comprising, after positioning the plurality of continuousplies and the plurality of drop-off plies in the stack, curing theplurality of continuous plies and the plurality of drop-off plies. 11.The method of claim 9, wherein positioning the plurality of continuousplies and the plurality of drop-off plies comprises positioning theplurality of continuous plies and the plurality of drop-off plies suchthat the plurality of drop-off plies are separated from each other by atleast one of the plurality of continuous plies.
 12. The method of claim9, wherein the central portion consists of at least one continuous plyof the plurality of continuous plies.
 13. The method of claim 9, whereinthe central portion comprises a single drop-off ply of the plurality ofdrop-off plies.
 14. A composite structure having a variable gage,comprising: a first segment having a first gage; a second segment havinga second gage, which is less than the first gage; and a transitionsegment between the first segment and the second segment, wherein thetransition segment comprises: a first end at the first segment andhaving the first gage, a second end at the second segment and having asecond gage, a first outer surface extending from the first end to thesecond end, a second outer surface extending from the first end to thesecond end, and a plurality of plies (i) extending between the first endand the second end and (ii) arranged in a stack between the first outersurface and the second outer surface, wherein the plurality of pliescomprise: a plurality of continuous plies, wherein each continuous plyextends from the first end to the second end, and a plurality ofdrop-off plies, wherein each drop-off ply comprises a tip having ablunt-end shape, wherein each drop-off ply extends from the first end toa respective position of the tip of the drop-off ply between the firstend and the second end, wherein a first subset of the plurality ofdrop-off plies are between the first outer surface and a central portionof the stack and a second subset of the plurality of drop-off plies arebetween the central portion and the second outer surface, wherein thetips of the plurality of drop-off plies are arranged in amonotonically-inward pattern comprising: (a) in a first order of thefirst subset of the plurality of drop-off plies from the first outersurface toward the central portion, with each successive drop-off ply inthe first order, a relative distance between the tip of the drop-off plyand the second end decreases, and (b) in a second order of the secondsubset of the plurality of drop-off plies from the second outer surfacetoward the central portion, with each successive drop-off ply in thesecond order, a relative distance between the tip of the drop-off plyand the second end decreases, wherein the first gage and the second gageare respective thicknesses between the first outer surface and thesecond outer surface at the first end and the second end, respectively,wherein the respective positions of the tips of the plurality ofdrop-off plies of the first subset are staggered with the respectivepositions of the tips of the plurality of drop-off plies of the secondsubset from the first end to the second end, wherein, for each drop-offply, a first distance between the tip of the drop-off ply and the tip ofan adjacent one of the plurality of drop-off plies is at least ten timesgreater than a thickness of the drop-off ply, wherein the first distanceis measured along the first end to the second end, wherein, for eachdrop-off ply, the adjacent one of the plurality of drop-off plies isadjacent to the drop-off ply in a dimension extending between the firstouter surface and the second outer surface, wherein a second distancebetween the tips of non-adjacent ones of the plurality of drop-off pliesis at least three times greater than a thickness of each drop-off ply,and wherein the second distance is measured along the first end to thesecond end.
 15. The composite structure of claim 14, wherein the firstsegment is a flange of a composite stringer and the second segment is aweb of the composite stringer.
 16. The composite structure of claim 14,wherein the plurality of drop-off plies are separated from each other byat least one of the plurality of continuous plies.
 17. The compositestructure of claim 14, wherein the central portion consists of at leastone continuous ply of the plurality of continuous plies.
 18. Thecomposite structure of claim 14, wherein the central portion comprises asingle drop-off ply of the plurality of drop-off plies.
 19. Thecomposite structure of claim 14, wherein the monotonically-inwardpattern further comprises, along a direction from the first end to thesecond end, the tips of the first subset of the plurality of drop-offplies alternating with the tips of the second subset of the plurality ofdrop-off plies.
 20. The composite structure of claim 14, wherein theplurality of drop-off plies are arranged in a plurality of pairs ofdrop-off plies, wherein each pair of drop-off plies comprises arespective one drop-off ply of the first subset and a respective onedrop-off ply of the second subset, and wherein, for each pair ofdrop-off plies, the respective one drop-off ply of the first subset andthe respective one drop-off ply of the second subset are substantiallyequidistant from the central portion in a dimension between the firstouter surface and the second outer surface.